1,174 results
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2. Reaction barriers on non-conducting surfaces beyond periodic local MP2: Diffusion of hydrogen on α-Al2O3(0001) as a test case.
- Author
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Mullan, Thomas, Maschio, Lorenzo, Saalfrank, Peter, and Usvyat, Denis
- Subjects
DENSITY functional theory ,WAVE functions ,APPROXIMATION error ,HYDROGEN ,FUNCTIONALS - Abstract
The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a α-Al
2 O3 (0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree–Fock and local Møller–Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72 eV): the correction to the frozen core-approximation of 0.06 eV and the CCSD(T) correction of 0.07 eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
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3. An analysis of quantum effects on the thermodynamic properties of cryogenic hydrogen using the path integral method.
- Author
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Nagashima, H., Tsuda, S., Tsuboi, N., Koshi, M., Hayashi, K. A., and Tokumasu, T.
- Subjects
HYDROGEN ,THERMODYNAMICS ,PATH integrals ,MOLECULAR dynamics ,EQUATIONS of state - Abstract
In this paper, we describe the analysis of the thermodynamic properties of cryogenic hydrogen using classical molecular dynamics (MD) and path integral MD (PIMD) method to understand the effects of the quantum nature of hydrogen molecules. We performed constant NVE MD simulations across a wide density-temperature region to establish an equation of state (EOS). Moreover, the quantum effect on the difference of molecular mechanism of pressure-volume-temperature relationship was addressed. The EOS was derived based on the classical mechanism idea only using the MD simulation results. Simulation results were compared with each MD method and experimental data. As a result, it was confirmed that although the EOS on the basis of classical MD cannot reproduce the experimental data of saturation property of hydrogen in the high-density region, the EOS on the basis of PIMD well reproduces those thermodynamic properties of hydrogen. Moreover, it was clarified that taking quantum effects into account makes the repulsion force larger and the potential well shallower. Because of this mechanism, the intermolecular interaction of hydrogen molecules diminishes and the virial pressure increases. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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4. Density functional theory investigation of H adsorption on the basal plane of boron-doped graphite.
- Author
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Ferro, Y., Marinelli, F., Allouche, A., and Brosset, C.
- Subjects
DENSITY functionals ,HYDROGEN ,GRAPHITE - Abstract
The scope of this paper is the theoretical study of hydrogen atom interaction with the boron-doped graphite surface taken as a model for the interactions that occur in controlled thermonuclear fusion devices. This work is carried out in the framework of the density functional theory. The boron-doped graphite surfaces are modeled using a small modified C[sub 16]H[sub 10] cluster, in which one or two carbon atoms are substituted by boron. The efficiency of the C[sub 16]H[sub 10] cluster in modeling the H-graphite interaction has already been established in a previous paper [J. Chem. Phys. 116, 8124 (2002)]. In this study, we show that the boron atom: (i) is not a stable adsorption site for H, that it induces (ii) an increase in the H binding energy, (iii) an increase in the permeability to H of the boron-doped graphite layer, and (iv) a long range electronic perturbation in its graphitic environment. A good agreement is found between our results and experimental studies dealing with erosion mechanisms of boron-doped graphite exposed to incident hydrogen ions fluxes. [ABSTRACT FROM AUTHOR]
- Published
- 2003
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5. Theoretical study of the unimolecular dissociation HO2→H+O2. II. Calculation of resonant states, dissociation rates, and O2 product state distributions.
- Author
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Dobbyn, Abigail J., Stumpf, Michael, Keller, Hans-Martin, and Schinke, Reinhard
- Subjects
UNIMOLECULAR reactions ,DISSOCIATION (Chemistry) ,HYDROGEN ,OXYGEN - Abstract
Three-dimensional quantum mechanical calculations have been carried out, using a modification of the log-derivative version of Kohn’s variational principle, to study the dissociation of HO2 into H and O2. In a previous paper, over 360 bound states were found for each parity, and these are shown to extend into the continuum, forming many resonant states. Analysis of the bound states close to the dissociation threshold have revealed that HO2 is a mainly irregular system and in this paper it is demonstrated how this irregularity persists in the continuum. At low energies above the threshold, these resonances are isolated and have widths that fluctuate strongly over more than two orders of magnitude. At higher energies, the resonances begin to overlap, while the fluctuations in the widths decrease. The fluctuations in the lifetimes and the intensities in an absorption-type spectrum are compared to the predictions of random matrix theory, and are found to be in fair agreement. The Rampsberger–Rice–Kassel–Marcus (RRKM) rates, calculated using variational transition state theory, compare well to the average of the quantum mechanical rates. The vibrational/rotational state distributions of O2 show strong fluctuations in the same way as the dissociation rates. However, their averages do not agree well with the predictions of statistical models, neither phase space theory (PST) nor the statistical adiabatic channel model (SACM), as these are dependent on the dynamical features of the exit channel. The results of classical trajectory calculations agree well on average with those of the quantum calculations. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 1996
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6. Adiabatic representations for the study of flux redistribution during photodissociation involving coupled electronic states: The effect of vibrational excitation on the photofragmentation of CH3I.
- Author
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Rist, Claire and Alexander, Millard H.
- Subjects
CHLORINE compounds ,HYDROGEN ,ADIABATIC invariants ,PHOTODISSOCIATION - Abstract
In this paper we exploit a method for the time-independent study of the growth of photofragment flux, governed by photon absorption, and the subsequent redistribution of the flux, governed by the Hamiltonian in the excited, unbound state. For dissociation involving multiple electronic states, each with internal (vibrational or rovibrational) degrees of freedom, from a mechanistic standpoint it is more revealing to analyze the flux in a basis which is adiabatic in the nuclear degrees of freedom but diabatic in the electronic degrees of freedom. This approach is pursued here in application to a two-dimensional model for the photodissociation of CH3I. [ABSTRACT FROM AUTHOR]
- Published
- 1993
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7. Rigid bender analysis of van der Waals complexes: The intermolecular bending potential of a hydrogen bond.
- Author
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Nesbitt, David J. and Lovejoy, Christopher M.
- Subjects
RIGID dynamics ,QUASIMOLECULES ,HYDROGEN ,CHEMICAL bonds - Abstract
High resolution ir data on weakly bound OCOHF complexes formed in a slit supersonic expansion reveal a progression of extremely low frequency vibrational levels associated with the bending of the OCO–HF hydrogen bond. In a previous paper [J. Chem. Phys. 93, 7716 (1990)], we presented a spectroscopic analysis of the fundamental, combination and hot bands observed, corresponding to transitions between vlbend=00, 11, 20, 22, and 31, where vlbend denotes quanta of OCOHF skeletal bend excitation with l units of vibrational angular momentum. In this paper, we analyze the rotationally resolved data in terms of the rigid bender formalism of Hougen, Bunker and Johns to determine an explicit angular potential, V(θ), for the OCOHF complex in both the HF ground (vHF=0) and vibrationally excited (vHF=1) state.The OCOHF ground state (vHF=0) potential is dominated by quartic and sextic angular terms, and thus is surprisingly shallow with respect to the bending angle. This quasilinear vibrational behavior is characterized by wide amplitude bending wave functions with zero point motion extending from -38° to +38°. In contrast, the OCOHF excited state (vHF=1) exhibits a significantly bent equilibrium geometry with a hydrogen bond bend angle of 31°±5°, corresponding to a cylindrically symmetric, noncolinear minimum in the potential. This shift in equilibrium geometry upon vHF excitation is quantitatively responsible for promoting Δvbend=0,2,... combination band vibrational modes, in analogy with Franck–Condon progressions in a bent←linear electronic transition.The predissociation lifetimes for vHF=1 excited OCOHF vary systematically with vlbend, and can be analyzed in terms of a geometry dependent predissociation rate which increases with bending of the hydrogen bond angle. These empirical bending potentials are in qualitative agreement with, but quantitatively much shallower than predicted by previous electrostatic and ab... [ABSTRACT FROM AUTHOR]
- Published
- 1992
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8. Cage occupancies, lattice constants, and guest chemical potentials for structure II hydrogen clathrate hydrate from Gibbs ensemble Monte Carlo simulations.
- Author
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Brumby, Paul E., Yuhara, Daisuke, Hasegawa, Tomohiro, Wu, David T., Sum, Amadeu K., and Yasuoka, Kenji
- Subjects
MONTE Carlo method ,GAS hydrates ,CHEMICAL potential ,LATTICE constants ,CHEMICAL structure ,HYDROGEN - Abstract
In this paper, equilibrium properties of structure II hydrates of hydrogen were determined from Monte Carlo simulations in the isothermal-isobaric Gibbs ensemble. Water and hydrogen molecules are described by the TIP4P/Ice and Silvera-Goldman models, respectively. The use of the Gibbs ensemble has many key advantages for the simulation of hydrates. By the separation of hydrogen vapor and hydrate phases into their own domains, coupled with transfer moves of hydrogen molecules between domains, cage occupancies were determined. Furthermore, the choice of this ensemble also allows equilibrium lattice constants and guest molecule chemical potentials to be straightforwardly estimated. Results for hydrogen mass fractions indicate reasonable agreement with prior simulation data and theoretical models, while detailed analysis of cage occupancy distributions and neighboring cage pair occupancy combinations gives valuable insight into the behavior of this hydrate at the inter-cage scale. These results will aid in the construction of theoretical models, for which knowledge of the occupancy of neighboring cages is of great importance. In support of previous experimental and theoretical works, we also find evidence of double occupancy of a few small cages inside of the hydrate stability zone, albeit at very high pressures; approximately 0.1% of small cages are doubly occupied at 300 MPa, for temperatures of 225 K and 250 K. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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9. Bimolecular reaction rates from ring polymer molecular dynamics: Application to H + CH4→ H2 + CH3.
- Author
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Suleimanov, Yury V., Collepardo-Guevara, Rosana, and Manolopoulos, David E.
- Subjects
CHEMICAL kinetics ,POLYMERS ,MOLECULAR dynamics ,HYDROGEN ,METHANE ,METHYL groups ,ATOM-atom collisions - Abstract
In a recent paper, we have developed an efficient implementation of the ring polymer molecular dynamics (RPMD) method for calculating bimolecular chemical reaction rates in the gas phase, and illustrated it with applications to some benchmark atom-diatom reactions. In this paper, we show that the same methodology can readily be used to treat more complex polyatomic reactions in their full dimensionality, such as the hydrogen abstraction reaction from methane, H + CH
4 → H2 + CH3 . The present calculations were carried out using a modified and recalibrated version of the Jordan-Gilbert potential energy surface. The thermal rate coefficients obtained between 200 and 2000 K are presented and compared with previous results for the same potential energy surface. Throughout the temperature range that is available for comparison, the RPMD approximation gives better agreement with accurate quantum mechanical (multiconfigurational time-dependent Hartree) calculations than do either the centroid density version of quantum transition state theory (QTST) or the quantum instanton (QI) model. The RPMD rate coefficients are within a factor of 2 of the exact quantum mechanical rate coefficients at temperatures in the deep tunneling regime. These results indicate that our previous assessment of the accuracy of the RPMD approximation for atom-diatom reactions remains valid for more complex polyatomic reactions. They also suggest that the sensitivity of the QTST and QI rate coefficients to the choice of the transition state dividing surface becomes more of an issue as the dimensionality of the reaction increases. [ABSTRACT FROM AUTHOR]- Published
- 2011
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10. Multiplexed polarization spectroscopy: Measuring surface hyperpolarizability orientation.
- Author
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Shultz, Mary Jane, Bisson, Patrick, Groenzin, Henning, and Li, Irene
- Subjects
POLARIZATION spectroscopy ,SUBSTRATES (Materials science) ,MESOMERISM ,HYDROGEN ,QUADRUPOLES ,HYDROGEN bonding ,ACETONITRILE - Abstract
Infrared-visible sum frequency generation (SFG) has seen increasing usage as a surface probe, particularly for liquid interfaces since they are amenable to few alternate probes. Interpreting the SFG data to arrive at a molecular-level configuration on the surface, however, remains a challenge. This paper reports a technique for analyzing and interpreting SFG data—called polarization-angle null or PAN-SFG. PAN-SFG enables ready identification of the ratio of the surface tangential and longitudinal hyperpolarizabilities—the hyperpolarizability direction—as well as the phase relationship between these components separated from the optical factors due to the substrate and experimental geometry. Separation of the surface optical factors results in an immediate connection between the null angle and the surface species polarization. If the Raman polarizability is also known, then PAN-SFG analysis, like the previously reported null techniques, provides a very accurate orientation. In addition, the reported polarization-angle, phase-shift analysis enables facile separation of the nonresonant background polarization from that of the resonant signal. Beyond orientation, PAN-SFG can be used to deconvolute overlapping resonances and identify components beyond a dipole response. This paper reports PAN-SFG for two systems providing deeper insight into both. An acetonitrile-water mixture was previously reported to undergo a phase transition at 7 mol %, attributed to a sudden change in orientation. PAN-SFG demonstrates that acetonitrile generates a classic dipole response and provides compelling evidence that the acetonitrile configuration remains constant as a function of concentration. An alternate model for the phase transition is presented. Like many aqueous systems, the SFG spectrum of the hydrogen-bonded region of ice consists of broad and overlapping features; features previously identified with PAN-SFG. Here PAN-SFG analysis is used to show that the reddest of these, the feature at 3098 cm
-1 , contains a significant quadrupole contribution that grows as the temperature is lowered. The quadrupole and its temperature dependence are used to assign the 3098 cm-1 feature to bilayer-stitching-hydrogen bonds. This is the first definitive assignment in the hydrogen-bonded region of water. [ABSTRACT FROM AUTHOR]- Published
- 2010
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11. Fluid variational theory for pressure dissociation in dense hydrogen: Multicomponent reference system and nonadditivity effects.
- Author
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Juranek, Hauke, Redmer, Ronald, and Rosenfeld, Yaakov
- Subjects
HYDROGEN ,FLUIDS ,PRESSURE - Abstract
In a recent paper, standard hard-sphere variational theory has been applied to pressure dissociation in dense fluid hydrogen (Juranek and Redmer, J. Chem. Phys. 112, 3780 (2000)). The correlation contributions to the dissociation equilibrium were determined from the free energy functional using effective pair potentials and minimization with respect to the hard-sphere reference system. For simplicity, the Berthelot mixing rule was used to determine the H-H[sub 2] pair potential (which entails additive effective hard spheres), and single-component reference pair correlation functions were employed for evaluating the correlation integrals. In this paper, we employ multicomponent reference pair correlations, and we study the sensitivity of the results with respect to nonadditivity of the effective hard spheres. We compare our results with available ab initio simulation data. [ABSTRACT FROM AUTHOR]
- Published
- 2002
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12. Spin switch in iron phthalocyanine on Au(111) surface by hydrogen adsorption.
- Author
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Yu Wang, Xiaoguang Li, Xiao Zheng, and Jinlong Yang
- Subjects
MOLECULAR physics ,IRON ,MOLECULAR dynamics ,PHTHALOCYANINES ,HYDROGEN ,ADSORPTION (Chemistry) - Abstract
The manipulation of spin states at the molecular scale is of fundamental importance for the development of molecular spintronic devices. One of the feasible approaches for the modification of a molecular spin state is through the adsorption of certain specific atoms or molecules including H, NO, CO, NH
3 , and O2 . In this paper, we demonstrate that the local spin state of an individual iron phthalocyanine (FePc) molecule adsorbed on an Au(111) surface exhibits controllable switching by hydrogen adsorption, as evidenced by using first-principles calculations based on density functional theory. Our theoretical calculations indicate that different numbers of hydrogen adsorbed at the pyridinic N sites of the FePc molecule largely modify the structural and electronic properties of the FePc/Au(111) composite by forming extra N-H bonds. In particular, the adsorption of one or up to three hydrogen atoms induces a redistribution of charge (spin) density within the FePc molecule, and hence a switching to a lowspin state (S = 1/2) from an intermediate spin state (S = 1) is achieved, while the adsorption of four hydrogen atoms distorts the molecular conformation by increasing Fe-N bond lengths in FePc and thus breaks the ligand field exerted on the Fe 3d orbitals via stronger hybridization with the substrate, leading to an opposite switching to a high-spin state (S = 2). These findings obtained from the theoretical simulations could be useful for experimental manipulation or design of single-molecule spintronic devices. [ABSTRACT FROM AUTHOR]- Published
- 2017
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13. Quantum reactive scattering with a deep well: Time-dependent calculation for H+O2 reaction and bound state characterization for HO2.
- Author
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Zhang, Dong H. and Zhang, John Z. H.
- Subjects
WAVE packets ,CHEMICAL reactions ,HYDROGEN ,OXYGEN ,BOUND states - Abstract
We show in this paper a time-dependent (TD) quantum wave packet calculation for the combustion reaction H+O2 using the DMBE IV (double many-body expansion) potential energy surface which has a deep well and supports long-lived resonances. The reaction probabilities from the initial states of H+O2(3Σ-g) (v=0–3, j=1) for total angular momentum J=0 are obtained for scattering energies from threshold up to 2.5 eV, which show numerous resonance features. Our results show that, by carrying out the wave packet propagation to several picoseconds, one can resolve essentially all the resonance features for this reaction. The present TD results are in good agreement with other time-independent calculations. A particular advantage of the time-dependent approach to this reaction is that resonance structures—strong energy dependence of the reaction probability—can be mapped out in a single wave packet propagation without having to repeat scattering calculations for hundreds of energies. We also report calculations of some low-lying vibrational energies of the hydroperoxyl radical HO2(2A‘) and their spectroscopic assignments. The vibrational frequencies of HO2(2A‘) on the DMBE IV potential energy surface are lower than experimental values, indicating the need to further improve the accuracy of the potential energy surface. [ABSTRACT FROM AUTHOR]
- Published
- 1994
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14. Accurate quantum calculations for H2+OH→H2O+H: Reaction probabilities, cross sections, and rate constants.
- Author
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Zhang, Dong H. and Zhang, John Z. H.
- Subjects
QUANTUM theory ,PROBABILITY theory ,HYDROGEN ,OXYGEN - Abstract
Following a previous Communication [J. Chem. Phys. 99, 5615 (1993)], which reported several initial state-selected total reaction probabilities for the title reaction for J=0, we present in this paper the methodologies of the previous calculation and show results of new calculations. In particular, the present calculations are extended to all angular momentum J>=0 and obtained reaction cross sections for a range of energies using the centrifugal sudden (CS) approximation. The computed cross sections are used to obtain the state-specific thermal rate constants for both the ground and the excited vibrations of H2. The dynamics calculation, in which the nonreactive OH bond is frozen, includes explicitly five degrees of freedom in the time-dependent quantum dynamics treatment. The comparison of the present accurate cross sections with other approximate theoretical calculations shows discrepancies. The computed rate constants (from the ground rotation state) are larger than experimental measurements at low temperatures, the v=0 rate is larger than the corresponding experimental rate by a factor of 1.8, and the ratio of v=1 to v=0 rate is a factor of 4.8 greater than the experimental ratio at 300 K. The calculated reaction rates are also compared to those of other theoretical calculations and the differences are discussed in the text. [ABSTRACT FROM AUTHOR]
- Published
- 1994
- Full Text
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15. Theoretical model for the dynamics of hydrogen recombination on the Si(100)-(2×1) surface.
- Author
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Sheng, Jia and Zhang, John Z. H.
- Subjects
DYNAMICS ,IONIZATION (Atomic physics) ,HYDROGEN - Abstract
We propose in this paper a quantitative theoretical model to describe the recombination dynamics of hydrogen on Si(100)-(2×1) surface. The desorption kinetics of hydrogen on Si(100) has been experimentally determined to obey a first-order rate law and the internal state distributions of desorbed hydrogen has recently been determined experimentally using the resonantly enhanced multiphoton ionization technique. In this theoretical model, which has the characteristic of preassociative desorption, the rate of desorption and the internal state distribution of H2 is given by a thermally averaged golden-rule expression. In particular, the desorption of H2 is supposed to result from a bound-free transition between an initially bound state composed of two H–Si dangling bonds on the same silicon dimer and a final continuum state consisting of H2 plus Si surface. In addition to explaining the first-order desorption kinetics, our model dictates that H2 will be vibrationally hot upon desorption, whereas rotation of H2 will generally be expected to be cold because of symmetry constraints. These conclusions about the dynamics are consistent with recent experiments [K. W. Kolasinski, S. F. Shane, R. N. Zare, J. Chem. Phys. 95, 5482 (1991); 96, 3995 (1992)] in which hydrogen is found to be vibrationally excited but rotationally cold. We show, in this paper, that essentially all recent experimental results on hydrogen desorption on Si(100) can be qualitatively explained based on the Franck–Condon factors in our model. A co-planar model calculation is carried out using our method, and the calculated rovibrational distribution of H2 is compared with the aforementioned experimental results of Kolasinski, Shane, and Zare. [ABSTRACT FROM AUTHOR]
- Published
- 1992
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16. Multiphoton ionization studies of C6H6–(CH3OH)n clusters. II. Intracluster ion–molecule reactions.
- Author
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Garrett, Aaron W. and Zwier, Timothy S.
- Subjects
MULTIPHOTON processes ,IONIZATION (Atomic physics) ,MOLECULES ,CARBON ,HYDROGEN - Abstract
The neutral C6H6–(CH3OH)n clusters, which have been spectroscopically characterized in Paper I, serve here as precursors for the study of intracluster ion chemistry initiated by resonant two-photon ionization. Resonant enhancement allows ion chemistry product yields to be determined as a function of cluster size by selective excitation of a single size cluster with the laser. Most of the work presented here uses one-color resonant ionization via the 610 transition of the C6H6 chromophore in the cluster. No ion chemistry is observed for the 1:n clusters with n≤2. At n=3, dissociative electron transfer (DET) to form C6H6+M+3 (M=CH3OH) is observed with a product yield of 6%. The remaining 94% of ionic products result from fragmentation of the 1:3 cluster by loss of a single CH3OH molecule. The unprotonated M+3 product ion is unusual in that electron bombardment or photoionization of pure methanol clusters yields exclusively protonated methanol cluster ions. The attachment of a C6H6 molecule to the methanol cluster provides an extremely gentle photoionization mechanism which produces M+3 with little enough internal energy to preclude its breakup to M2H++CH2OH (or CH3O ). The opening of this product channel at n=3 is consistent with estimates of the ionization potential of Mn clusters which predict an endothermic ET reaction at n=2 which becomes exothermic at n=3.Despite the increasingly exothermic DET and dissociative proton transfer product channels, larger clusters (n≥4) continue to predominantly undergo unreactive fragmentation. For the 1:4 and 1:5 clusters, in addition to DET products, dissociative proton transfer (DPT) products are also observed. The MnH+ product arises from proton transfer from C6H+6, while Mn-1H+ probably occurs by DPT within the M+n cluster following loss of C6H6 in DET. Scans of the 1:2–1:5 clusters through their 610110 transitions yield a broader set of products which reflect the 5 kcal/mol increase in the... [ABSTRACT FROM AUTHOR]
- Published
- 1992
- Full Text
- View/download PDF
17. Accurate ab initio potential energy computations for the H4 system: Tests of some analytic potential energy surfaces.
- Author
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Boothroyd, Arnold I., Dove, John E., Keogh, William J., Martin, Peter G., and Peterson, Michael R.
- Subjects
POTENTIAL energy surfaces ,HYDROGEN - Abstract
The interaction potential energy surface (PES) of H4 is of great importance for quantum chemistry, as a test case for molecule–molecule interactions. It is also required for a detailed understanding of certain astrophysical processes, namely, collisional excitation and dissociation of H2 in molecular clouds, at densities too low to be accessible experimentally. Accurate ab initio energies were computed for 6046 conformations of H4, using a multiple reference (single and) double excitation configuration interaction (MRD-CI) program. Both systematic and ‘‘random’’ errors were estimated to have an rms size of 0.6 mhartree, for a total rms error of about 0.9 mhartree (or 0.55 kcal/mol) in the final ab initio energy values. It proved possible to include in a self-consistent way ab initio energies calculated by Schwenke, bringing the number of H4 conformations to 6101. Ab initio energies were also computed for 404 conformations of H3; adding ab initio energies calculated by other authors yielded a total of 772 conformations of H3. (The H3 results, and an improved analytic PES for H3, are reported elsewhere.) Ab initio energies are tabulated in this paper only for a sample of H4 conformations; a full list of all 6101 conformations of H4 (and 772 conformations of H3 ) is available from Physics Auxiliary Publication Service (PAPS), or from the authors.The best existing analytic PESs for H4 are shown to be accurate only for pairs of H2 molecules with intermolecular separations greater than about 3 bohr (1.6 Å). High energy collisions (such as might lead to direct collisional dissociation) cannot be well represented by such surfaces. A more general analytic PES for H4 is required, which will be accurate for compact (high-energy) conformations and for conformations that cannot be subdivided into a pair of H2 molecules. Work in progress on devising such a surface (fitted to the 6101 conformations of this work) will be reported in a... [ABSTRACT FROM AUTHOR]
- Published
- 1991
- Full Text
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18. Equation of state and force fields for Feynman–Hibbs-corrected Mie fluids. II. Application to mixtures of helium, neon, hydrogen, and deuterium.
- Author
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Aasen, Ailo, Hammer, Morten, Müller, Erich A., and Wilhelmsen, Øivind
- Subjects
NEON ,EQUATIONS of state ,DEUTERIUM ,HELIUM ,HELMHOLTZ free energy ,MIE scattering ,HYDROGEN ,CUBIC equations ,QUANTUM theory - Abstract
We extend the statistical associating fluid theory of quantum corrected Mie potentials (SAFT-VRQ Mie), previously developed for pure fluids [Aasen et al., J. Chem. Phys. 151, 064508 (2019)], to fluid mixtures. In this model, particles interact via Mie potentials with Feynman–Hibbs quantum corrections of first order (Mie-FH1) or second order (Mie-FH2). This is done using a third-order Barker–Henderson expansion of the Helmholtz energy from a non-additive hard-sphere reference system. We survey existing experimental measurements and ab initio calculations of thermodynamic properties of mixtures of neon, helium, deuterium, and hydrogen and use them to optimize the Mie-FH1 and Mie-FH2 force fields for binary interactions. Simulations employing the optimized force fields are shown to follow the experimental results closely over the entire phase envelopes. SAFT-VRQ Mie reproduces results from simulations employing these force fields, with the exception of near-critical states for mixtures containing helium. This breakdown is explained in terms of the extremely low dispersive energy of helium and the challenges inherent in current implementations of the Barker–Henderson expansion for mixtures. The interaction parameters of two cubic equations of state (Soave–Redlich–Kwong and Peng–Robinson) are also fitted to experiments and used as performance benchmarks. There are large gaps in the ranges and properties that have been experimentally measured for these systems, making the force fields presented especially useful. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
19. Methanol synthesis on Zn0(0001). IV. Reaction mechanisms and electronic structure.
- Author
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Frenzel, Johannes and Marx, Dominik
- Subjects
METHANOL ,CHEMICAL synthesis ,CARBON monoxide ,HYDROGEN ,GAS phase reactions ,MOLECULAR dynamics ,ZINC oxide ,ELECTRONIC structure - Abstract
Methanol synthesis from CO and H
2 over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partially hydroxylated and defective ZnO(0001) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving "near-surface" molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H2 stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive electronic structure analysis. [ABSTRACT FROM AUTHOR]- Published
- 2014
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20. The tensor hypercontracted parametric reduced density matrix algorithm: Coupled-cluster accuracy with O(r4) scaling.
- Author
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Shenvi, Neil, van Aggelen, Helen, Yang, Yang, Yang, Weitao, Schwerdtfeger, Christine, and Mazziotti, David
- Subjects
DENSITY matrices ,TENSOR algebra ,ELECTRONS ,ELECTRONIC excitation ,ALGORITHMS ,ALKANES ,HYDROGEN ,WAVE functions - Abstract
Tensor hypercontraction is a method that allows the representation of a high-rank tensor as a product of lower-rank tensors. In this paper, we show how tensor hypercontraction can be applied to both the electron repulsion integral tensor and the two-particle excitation amplitudes used in the parametric 2-electron reduced density matrix (p2RDM) algorithm. Because only O(r) auxiliary functions are needed in both of these approximations, our overall algorithm can be shown to scale as O(r4), where r is the number of single-particle basis functions. We apply our algorithm to several small molecules, hydrogen chains, and alkanes to demonstrate its low formal scaling and practical utility. Provided we use enough auxiliary functions, we obtain accuracy similar to that of the standard p2RDM algorithm, somewhere between that of CCSD and CCSD(T). [ABSTRACT FROM AUTHOR]
- Published
- 2013
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21. On the formation of hydrogen gas on copper in anoxic water.
- Author
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Johansson, Adam Johannes, Lilja, Christina, and Brinck, Tore
- Subjects
HYDROGEN ,COPPER ,ANOXIC zones ,CORROSION & anti-corrosives ,THERMODYNAMICS ,SURFACE chemistry ,SOLVENTS ,ACTIVATION (Chemistry) ,GIBBS' free energy - Abstract
Hydrogen gas has been detected in a closed system containing copper and pure anoxic water [P. Szakalos, G. Hultquist, and G. Wikmark, Electrochem. Solid-State Lett. 10, C63 (2007) and G. Hultquist, P. Szakalos, M. Graham, A. Belonoshko, G. Sproule, L. Grasjo, P. Dorogokupets, B. Danilov, T. Aastrup, G. Wikmark, G. Chuah, J. Eriksson, and A. Rosengren, Catal. Lett. 132, 311 (2009)]. Although bulk corrosion into any of the known phases of copper is thermodynamically forbidden, the present paper shows how surface reactions lead to the formation of hydrogen gas in limited amounts. While water cleavage on copper has been reported and investigated before, formation of molecular hydrogen at a single-crystal Cu[100] surface is here explored using density functional theory and transition state theory. It is found that although solvent catalysis seems possible, the fastest route to the formation of molecular hydrogen is the direct combination of hydrogen atoms on the copper surface. The activation free energy (▵Gs‡f) of hydrogen formation in condensed phase is 0.70 eV, which corresponds to a rate constant of 10 s-1 at 298.15 K, i.e., a relatively rapid process. It is estimated that at least 2.4 ng hydrogen gas could form per cm2 on a perfect copper surface. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
22. Theoretical study of the rovibrational spectrum of H2O-H2.
- Author
-
Wang, Xiao-Gang and Carrington, Tucker
- Subjects
VIBRATIONAL spectra ,HYDROGEN ,OXYGEN ,PHYSICS experiments ,SYMMETRY (Physics) ,ALGORITHMS ,POTENTIAL theory (Physics) ,PROTONS - Abstract
In this paper we report transition frequencies and line strengths computed for H
2 O-H2 and compare with the experimental observations of [M. J. Weida and D. J. Nesbitt, J. Chem. Phys. 110, 156 (1999)]. To compute the spectra we use a symmetry adapted Lanczos algorithm and an uncoupled product basis set. Our results corroborate the assignments of Weida and Nesbitt and there is good agreement between calculated and observed transitions. Possible candidates for lines that Weida and Nesbitt were not able to assign are presented. Several other bands that may be observable are also discovered. Although all the observed bands are associated with states localized near the global potential minimum, at which H2 O acts as proton acceptor, a state with significant amplitude near the T-shape secondary potential minimum at which H2 O acts as proton donor is identified by examining many different probability density plots. [ABSTRACT FROM AUTHOR]- Published
- 2011
- Full Text
- View/download PDF
23. Toward spectroscopic accuracy for open-shell systems: Molecular structure and hyperfine coupling constants of H2CN, H2CP, NH2, and PH2 as test cases.
- Author
-
Puzzarini, Cristina and Barone, Vincenzo
- Subjects
MOLECULAR structure ,COUPLING constants ,BASIS sets (Quantum mechanics) ,EXTRAPOLATION ,HYPERFINE structure ,HYDROGEN ,RADICALS (Chemistry) ,ELECTRONIC excitation - Abstract
In the present paper, we investigate the molecular structure and hyperfine couplings of a series of σ radicals containing first- and second-row atoms (H
2 CN,H2 CP,NH2 ,PH2 ) for which accurate gas-phase microwave results are available. The presence of α- and, especially, β-hydrogen atoms makes the evaluation of magnetic properties of these radicals particularly challenging. Geometrical parameters have been computed by the coupled-cluster ansatz in conjunction with hierarchical series of basis sets, thus accounting for extrapolation to the complete basis-set limit. Core correlation as well as higher excitations in the electronic-correlation treatment have also been taken into account. An analogous approach has been employed for evaluating hyperfine coupling constants with particular emphasis given to basis-set, correlation, and geometrical effects. The corresponding vibrational corrections, required for a meaningful comparison to experimental data, have also been investigated. The remarkable agreement with experiment confirms the reliability of the present computational approach, already validated for π radicals, thus establishing the way for setting up a benchmark database for magnetic properties. [ABSTRACT FROM AUTHOR]- Published
- 2010
- Full Text
- View/download PDF
24. A new electron-methanol molecule pseudopotential and its application for the solvated electron in methanol.
- Author
-
Mones, Letif and Turi, László
- Subjects
MOLECULES ,PSEUDOPOTENTIAL method ,METHANOL ,FORCE & energy ,HYDROGEN - Abstract
A new electron-methanol molecule pseudopotential is developed and tested in the present paper. The formal development of the potential is based on quantum mechanical calculations on the electron-methanol molecule model in the static exchange approximation. The computational model includes a steep confining potential that keeps the otherwise unbound excess electron in the vicinity of the methanol molecule. Using the Phillips–Kleinman theorem we introduce a smooth pseudowave function of the excess electron with the exact eigenenergy and correct asymptotic behavior. The nonlocal potential energy operator of the model Hamiltonian is then replaced to a local potential that reproduces the ground-state properties of the excess electron satisfactorily. The pseudopotential is then optimized in an analytically simple functional form to fit this approximate local potential in conjunction with the point charges and the geometry of a classical, all-site methanol-methanol interaction potential. Of the adjustable parameters, the parameters for the carbon and the methyl hydrogen atoms are optimized, while those for the oxygen and the hydroxyl hydrogen are taken from a previous electron-water molecule pseudopotential. A polarization term is added to the potential a posteriori. The polarization parameters are chosen to reproduce the experimental position of the optical absorption spectrum of an excess electron in mixed quantum-classical molecular dynamics simulations. The energetic, structural and spectroscopic properties of the solvated electron in a methanol bath are simulated at 300 K and compared with previous solvated electron simulations and available experimental data. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
25. An isolated line-shape model based on the Keilson–Storer function for velocity changes. II. Molecular dynamics simulations and the Q(1) lines for pure H2.
- Author
-
Tran, H., Hartmann, J.-M., Chaussard, F., and Gupta, M.
- Subjects
MOLECULAR dynamics ,SIMULATION methods & models ,SPEED ,HYDROGEN ,TEMPERATURE ,COLLISIONS (Physics) ,AUTOCORRELATION (Statistics) - Abstract
This paper presents comparisons between molecular dynamics simulations (MDSs) and the Keilson and Storer (KS) model for collision-induced translational velocity changes in pure H
2 at room temperature from four different points of view. The first considers various autocorrelation functions associated with the velocity. The second and third comparisons are made for the collision kernels and for the time evolutions of some conditional probabilities for changes in the velocity modulus and orientation. Finally, the evolutions, with density, of the half widths of the Q(1) lines of the isotropic Raman (1–0) fundamental band and of the (2–0) overtone quadrupole band are investigated. The results demonstrate that, while the KS approach gives a poor description of detailed velocity-to-velocity changes, it leads to accurate results for the correlation functions and spectral shapes, quantities resulting from large averages over the velocity. On the opposite, collision kernels derived from MDS lead to accurate predictions of all considered quantities. The results open promising perspectives for modeling of the spectral shapes of other systems. They also stress the value of direct calculations of speed-dependent broadening and shifting parameters from the intermolecular potential to avoid their determination from measured spectra and permit fully meaningful tests of the models. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
26. How silylene defects at (100) Si surfaces can account for the anomalous features observed via x-ray photoelectron spectroscopy.
- Author
-
Cerofolini, G. F., Giorgi, G., Sgamellotti, A., and Belanzoni, P.
- Subjects
HYDROGEN ,SILICON ,CHEMICAL reactions ,PHOTOELECTRON spectroscopy ,MOLECULAR spectroscopy - Abstract
A theoretical analysis of the hydrogen-terminated (100) surface of silicon leads to the identification of a new configuration, formed by a silylene center interacting with vicinal silicon dihydrides. This structure may be viewed as a metastable configuration of 2×1 (100) (SiH)
2 . Silylene can however be stabilized via interaction with water. The paper proposes that some of the anomalous features observed at the hydrogen-terminated or oxidized (100) Si can be attributed to silylene centers datively stabilized by oxo groups or to structures resulting from their decomposition. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
27. The hydrogen abstraction reaction H+CH4. II. Theoretical investigation of the kinetics and dynamics.
- Author
-
Espinosa-García, J., Nyman, G., and Corchado, J. C.
- Subjects
HYDROGEN ,QUANTUM theory ,SCATTERING (Physics) ,CHEMICAL reactions ,DYNAMICS ,NUCLEAR reactions - Abstract
On a new potential energy surface (PES-2008) developed by our group (preceding paper), we performed an extensive kinetics study using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range of 250–2000 K and a dynamics study using quasiclassical trajectory (QCT) and quantum-mechanical (QM) calculations at collision energies between 0.7 and 2.0 eV for the title reaction and isotopically substituted versions. Kinetically, the H+CH
4 forward and reverse thermal rate constants reproduce the available experimental data, with a small curvature of the Arrhenius plot indicating the role of tunneling in this hydrogen abstraction reaction. Five sets of kinetic isotope effects are also calculated. In general, they reproduce the experimental information. Dynamically, we focused on the H+CD4 reaction because there are more experimental studies for comparison. Most of the available energy appears as product translational energy (55%–68%), with the HD product being vibrationally cold (v′ =0,1) in agreement with experiment, although rotationally hotter than experiment. The reaction cross section is practically negligible at 0.7 eV and still small at 1.5 eV, reproducing the experimental evidence, although our values are smaller. The product angular distribution is analyzed using QCT and QM methods. While at low energies (0.7 eV) both the QCT and the QM calculations yield forward scattered CD3 product, i.e., a rebound mechanism, at high energy (1.2 eV) only the QM calculations reproduce the experiment. The agreement with this wide variety of kinetic and dynamic experimental data (always qualitative and in some cases quantitative) shows the capacity of the PES-2008 surface to describe the reaction system. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
28. Activation energies of sigmatropic shifts in propene and acetone enolate from the anti-Hermitian contracted Schrödinger equation.
- Author
-
Foley, Jonathan J., Rothman, Adam E., and Mazziotti, David A.
- Subjects
PROPENE ,ACETONE ,HYDROGEN ,CHEMICAL reactions ,PARTICLES (Nuclear physics) - Abstract
The hydrogen [1,3]-sigmatropic shift in propene is predicted by the Woodward–Hoffman rules to occur by an antarafacial pathway, yet the lack of experimental evidence suggests that this pathway is not favorable. Two natural questions arise: (i) can the [1,3]-shift be made more favorable by a symmetry-forbidden multistep pathway, and (ii) can the energetics be influenced by a substituent on propene? As in many chemical reactions, describing the energetics of these reactions requires a balanced treatment of both single-reference and multireference electron correlations, and yet traditional wave function methods often excel in treating only one kind of correlation. An equitable description of correlation effects, however, can be achieved, at a cost similar to efficient single-reference methods, by computing the two-electron reduced density matrix (2-RDM) from the anti-Hermitian part of the contracted Schrödinger equation (ACSE) [D. A. Mazziotti, Phys. Rev. Lett. 97, 143002 (2006)]. As with the contracted Schrödinger equation, the indeterminacy of the ACSE is removed without the many-electron wave function by reconstructing the 3-RDM from the 2-RDM via cumulant theory [D. A. Mazziotti, Chem. Phys. Lett. 289, 419 (1998)]. In this paper we apply the ACSE to study sigmatropic shifts in both propene and acetone enolate while extending its formalism to treat doublet spin states. In the 6-311G
** basis set the ACSE predicts the activation energy of the trimethylene-to-propene rearrangement to be 8.8 kcal/mol while multireference perturbation theory yields a smaller barrier of 2.2 kcal/mol and coupled cluster singles-doubles predicts a negative barrier. We further find that the [1,3]-shift in acetone enolate is more favorable by ≈30 kcal/mol than the [1,3]-shift in propene, which is consistent with a prior theoretical investigation as well as experimental observations of these shifts in 2-butanone enolate. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
29. Sum-frequency generation: Polarization surface spectroscopy analysis of the vibrational surface modes on the basal face of ice Ih.
- Author
-
Groenzin, Henning, Li, Irene, and Shultz, Mary Jane
- Subjects
SPECTRUM analysis ,SOLUTION (Chemistry) ,MOLECULES ,HYDROGEN ,RAMAN effect ,POLARIZABILITY (Electricity) - Abstract
In recent years, sum-frequency generation (SFG) has been used to investigate numerous interfaces including aqueous interfaces. A longstanding challenge to interpretation of the SFG results, along with the related aqueous-solution infrared and Raman spectra, is a lack of connection between features in the broad hydrogen-bonded region and molecular-level interactions or configurations. This paper reports results of a newly developed polarization analysis of the generated sum-frequency signal as a function of wavelength both to deconvolute spectral resonances and to characterize the dynamic polarization associated with the resonances. Operationally, the polarization angle of the generated sum frequency is determined by identifying the null angle. The technique is hence termed polarization-angle null analysis or PAN. PAN applied to ice is very powerful; it reveals that the hydrogen-bonded region of the basal face of ice I
h contains at least five oscillators, each with a distinct polarization. The dynamic polarizability of the longest wavelength oscillator is nearly entirely transverse (perpendicular to the surface normal, i.e., in the surface plane); in contrast, the shortest wavelength oscillator is almost entirely longitudinal (along the surface normal). [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
30. Structural, energetic, and electronic properties of hydrogenated titanium clusters.
- Author
-
Dhilip Kumar, T. J., Tarakeshwar, P., and Balakrishnan, N.
- Subjects
TITANIUM ,TITANIUM group ,TITANATES ,PHYSICAL & theoretical chemistry ,HYDROGEN ,SURFACE chemistry ,ELECTRONIC systems - Abstract
Hydrogen undergoes dissociative chemisorption on small titanium clusters. How the electronic structure of the cluster changes as a function of the number of adsorbed hydrogen atoms is an important issue in nanocatalysis and hydrogen storage. In this paper, a detailed theoretical investigation of the structural, energetic, and electronic properties of the icosahedral Ti
13 cluster is presented as a function of the number of adsorbed hydrogen atoms. The results show that hydrogen loaded Ti13 H20 and Ti13 H30 clusters are exceptionally stable and are characterized by hydrogen multicenter bonds. In Ti13 H20 , the dissociated hydrogen atoms are bound to each of the 20 triangular faces of Ti13 , while in Ti13 H30 , they are bound to the 30 Ti–Ti edges of Ti13 . Consequently, the chemisorption and desorption energies of the Ti13 H20 (1.93 eV, 3.10 eV) are higher than that of Ti13 H30 (1.13 eV, 1.95 eV). While increased hydrogen adsorption leads to an elongation of the Ti–Ti bonds, there is a concomitant increase in the electrostatic interaction between the dissociated hydrogen atoms and the Ti13 cluster. This enhanced interaction results from the participation of the subsurface titanium atom at higher hydrogen concentrations. Illustrative results of hydrogen saturation on the larger icosahedral Ti55 cluster are also discussed. The importance of these results on hydrogen saturated titanium clusters in elucidating the mechanism of hydrogen adsorption and desorption in titanium doped complex metal hydrides is discussed. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
31. Classical and quantum studies of the photodissociation of a HX (X=Cl,F) molecule adsorbed on ice.
- Author
-
Woittequand, S., Duflot, D., Monnerville, M., Pouilly, B., Toubin, C., Briquez, S., and Meyer, H.-D.
- Subjects
HYDROGEN ,PHOTODISSOCIATION ,ICE ,DISSOCIATION (Chemistry) ,POTENTIAL energy surfaces ,WAVE packets - Abstract
The photodissociation dynamics of a HX (X=Cl,F) molecule adsorbed on a hexagonal ice surface at T=0 K is studied using time-dependent quantum wave packets and quasiclassical trajectories. The relevant potential energy surfaces are calculated using high-level ab initio methods. We present here two dimensional calculations for the dynamics of the hydrogen photofragment for both HCl and HF molecules. The purpose of this paper is to compare the photodissociation dynamics of the two molecules which are adsorbed on the ice surface with different equilibrium geometries. The total photodissociation cross section and the angular distribution are calculated. The comparison with classical trajectory calculations provides evidence for typical quantum effects and reveals rainbow structures. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
32. Theoretical study of vibration-phonon coupling of H adsorbed on a Si(100) surface.
- Author
-
Andrianov, Ivan and Saalfrank, Peter
- Subjects
PERTURBATION theory ,DYNAMICS ,HYDROGEN ,CHEMICAL bonds ,CHEMICAL reactions ,PARTICLES (Nuclear physics) - Abstract
In this paper a perturbation-theory study of vibrational lifetimes for the bending and stretching modes of hydrogen adsorbed on a Si(100) surface is presented. The hydrogen-silicon interaction is treated with a semiempirical bond-order potential. Calculations are performed for H–Si clusters of different sizes. The finite lifetime is due to vibration-phonon coupling, which is assumed to be linear or bilinear in the phonon and nonlinear in the H–Si stretching and bending modes. Lifetimes and vibrational transition rates are evaluated with one- and two-phonon processes taken into account. Temperature effects are also discussed. In agreement with the experiment and previous theoretical treatment it is found that the H–Si (υ
s =1) stretching vibration decays on a nanosecond timescale, whereas for the H–Si (υb =1) bending mode a picosecond decay is predicted. For higher-excited vibrations, simple scaling laws are found if the excitation energies are not too large. The relaxation mechanisms for the excited H–Si stretching and the H–Si bending modes are analyzed in detail. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
33. The lowest triplet state [sup 3]A[sup ′] of H[sub 3][sup +]: Global potential energy surface and vibrational calculations.
- Author
-
Sanz, Cristina, Roncero, Octavio, Tablero, César, Aguado, Alfredo, and Paniagua, Miguel
- Subjects
HYDROGEN ,POTENTIAL energy surfaces ,ENERGY levels (Quantum mechanics) - Abstract
The adiabatic global potential energy surface of the H[sub 3][sup +] system for the lowest triplet excited state of A[sup ′] symmetry was computed for an extensive grid of conformations around the minimum region at full configuration interaction ab initio level, using a much more extended basis set than in a previous paper from the same authors. An accurate global fit (rms error lower than 27 cm[sup -1] for energies lower than dissociation into separated atoms and lower than 5 cm[sup -1] for energies lower than the dissociation channel) to these ab initio points and also to part of the previous calculated points (for a total of 7689 energies in the data set) of the lowest triplet excited state of A[sup ′] symmetry is obtained using a diatomics-in-molecules approach corrected by one symmetrized three-body term with a total of 109 linear parameters and 1 nonlinear parameter. This produces an accurate global potential which represents all aspects of the bound triplet excited state of H[sub 3][sup +] including the minima and dissociation limits, satisfying the correct symmetry properties of the system. The vibrational eigenstates have been calculated using hyperspherical coordinates with symmetry adapted basis functions with the proper regular behavior at the Eckart singularities. The accuracy of the vibrational levels thus obtained is expected to be better than 2 cm[sup -1] with respect to unknown experimental values. Due to the presence of three equivalent minima at collinear geometries (D[sub ∞h]) the lower vibrational levels are close to triple degenerate. Since the interconversion barrier between the three minima is about 2640 cm[sup -1], these states split for the upper excited vibrational levels. Such splitting can provide a key feature to identifying the unassigned transitions amongst the many H[sub 3][sup +] lines that have been observed in hydrogen plasmas. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2001
- Full Text
- View/download PDF
34. Evidence for hydrogen desorption through both interdimer and intradimer paths from Si(100)-(2×1).
- Author
-
Shi, J., Chuan Kang, H., Tok, E. S., and Zhang, J.
- Subjects
HYDROGEN ,THERMAL desorption ,NONMETALS ,MONTE Carlo method ,SURFACE chemistry ,LASERS - Abstract
Despite intensive work there are still controversial issues about desorption and adsorption of hydrogen on Si(100)-(2×1). In particular, the relative importance of the various interdimer- and intradimer-desorption paths is not clear. Nanosecond-pulse-laser desorption data have been used to argue that the 4H interdimer path is important, while data from thermal-desorption time-of-flight measurements suggest a large translationally hot contribution which cannot arise from the 4H interdimer path. The observation of a translationally hot desorption fraction at low to medium coverage can be accounted for by including the 2H interdimer path in quantum dynamical calculations. In this paper we investigate this issue further and present evidence that supports the inclusion of the intradimer path. Specifically, our results show that the intradimer and 3H interdimer paths provide the major contributions to the translationally hot fraction in the desorbate. Our conclusions are based on density-functional calculations of hydrogen translational excitation, mean-field analysis of thermal-desorption experiments over a range of ramp rate, and Monte Carlo simulations of nanosecond-pulse-laser experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
35. Analysis of the nuclear-electronic orbital method for model hydrogen transfer systems.
- Author
-
Swalina, Chet, Pak, Michael V., and Hammes-Schiffer, Sharon
- Subjects
ELECTRONIC systems ,HYDROGEN ,PARTICLES (Nuclear physics) ,CATHODE rays ,POTENTIAL energy surfaces ,QUANTUM chemistry - Abstract
Fundamental issues associated with the application of the nuclear-electronic orbital (NEO) approach to hydrogen transfer systems are addressed. In the NEO approach, specified nuclei are treated quantum mechanically on the same level as the electrons, and mixed nuclear-electronic wavefunctions are calculated with molecular orbital methods. The positions of the nuclear basis function centers are optimized variationally. In the application of the NEO approach to hydrogen transfer systems, the hydrogen nuclei and all electrons are treated quantum mechanically. Within the NEO framework, the transferring hydrogen atom can be represented by two basis function centers to allow delocalization of the proton vibrational wavefunction. In this paper, the NEO approach is applied to the [He-H-He]
+ and [He-H-He]++ model systems. Analyses of technical issues pertaining to flexibility of the basis set to describe both single and double well proton potential energy surfaces, linear dependency of the hydrogen basis functions, multiple minima in the basis function center optimization, convergence of the number of hydrogen basis function centers, and basis set superposition error are presented. The accuracy of the NEO approach is tested by comparison to grid calculations for these model systems. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
36. Numerical treatment discussion and ab initio computational reinvestigation of physisorption of molecular hydrogen on graphene.
- Author
-
Ferre-Vilaplana, A.
- Subjects
HYDROGEN ,GRAPHEMICS ,GRAPHOLOGY ,LINGUISTICS ,WRITING ,MILITARY strategy - Abstract
A numerical treatment suitable for the computational investigation of physisorption of molecular hydrogen on carbon nanostructures has not been sufficiently discussed. In this paper it is shown that results used as a reference are actually a product of poorly solved interactions and contaminated estimates with errors which would be of the order of 60%. Moreover, using ab initio molecular orbital theory, under the rigid monomer supermolecular approach, the physisorption energy of molecular hydrogen on graphene was reinvestigated. The graphene surface was modeled as a coronenelike (C
24 H12 ) graphene sheet. The basis set superposition error was corrected by means of the counterpoise method. The H2 –H2 and H2 -benzene interactions were examined, under systematic combinations of basis sets and correlation methods, including the aug-cc-pVQZ basis set and the coupled cluster correlation method with single, double, and noniterative triple excitations, searching for a numerical treatment with a reasonable trade-off between efficiency and accuracy. Asymmetrical modeling strategies, using diffusion augmented basis sets with preference for the adsorbate, were found to be effective. Also local modeling strategies, using more complete basis sets for the nearest atoms to the adsorbate than for the rest of the substrate, were considered. The aug-cc-pVTZ basis set for the adsorbate and for the nearest atoms to the adsorbate and the cc-pVTZ basis set for the rest of the cluster-modeled graphene, at the second-order Möller–Plesset perturbation theory correlation level, was selected as reference treatment. It was found that the physisorption energy of molecular hydrogen on graphene would be of the order of 0.06 eV, which would be 25% less than what has been previously published, though it would be sufficient to permit the storage of hydrogen physisorbed on carbon. To our knowledge this would be the most realistic theoretical estimate of the mentioned energy to date. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
37. Phase space conduits for reaction in multidimensional systems: HCN isomerization in three dimensions.
- Author
-
Waalkens, Holger, Burbanks, Andrew, and Wiggins, Stephen
- Subjects
ISOMERIZATION ,HYDROGEN ,CYANIDES ,DEGREES of freedom ,QUANTUM theory ,MOLECULAR dynamics - Abstract
The three-dimensional hydrogen cyanide/isocyanide isomerization problem is taken as an example to present a general theory for computing the phase space structures which govern classical reaction dynamics in systems with an arbitrary (finite) number of degrees of freedom. The theory, which is algorithmic in nature, comprises the construction of a dividing surface of minimal flux which is locally a ''surface of no return.'' The theory also allows for the computation of the global phase space transition pathways that trajectories must follow in order to react. The latter are enclosed by the stable and unstable manifolds of a so-called normally hyperbolic invariant manifold (NHIM). A detailed description of the geometrical structures and the resulting constraints on reaction dynamics is given, with particular emphasis on the three degrees of freedom case. A procedure is given which uses these structures to compute orbits homoclinic to, and heteroclinic between, NHIMs. The role of homoclinic and heteroclinic orbits in global recrossings of dividing surfaces and transport in complex systems is explained. The complete description provided here is inherently one within phase space; it cannot be inferred from a configuration space picture. A complexification of the classical phase space structures to incorporate quantum effects is also discussed. The results presented here call into question certain assumptions routinely made on the global dynamics; this paper provides methods that enable one to understand and quantify the phase space dynamics of reactions without making such assumptions. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
38. Real-time study of the adiabatic energy loss in an atomic collision with a metal cluster.
- Author
-
Baer, Roi and Siam, Nidal
- Subjects
ENERGY dissipation ,HYDROGEN ,METALLIC surfaces ,ELECTRONS ,ATOMS ,DENSITY functionals - Abstract
Gas-phase hydrogen atoms are accelerated towards metallic surfaces in their vicinity. As it approaches the surface, the velocity of an atom increases and this motion excites the metallic electrons, causing energy loss to the atom. This dissipative dynamics is frequently described as atomic motion under friction, where the friction coefficient is obtained from ab initio calculations assuming a weak interaction and slow atom. This paper tests the aforementioned approach by comparing to a real-time Ehrenfest molecular dynamics simulation of such a process. The electrons are treated realistically using standard approximations to time-dependent density functional theory. We find indeed that the electronic excitations produce a frictionlike force on the atom. However, the friction coefficient strongly depends on the direction of the motion of the atom: it is large when the atom is moving towards the cluster and much smaller when the atom is moving away. It is concluded that a revision of the model for energy dissipation at metallic surfaces, at least for clusters, may be necessary. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
39. Quantal density functional theory of the hydrogen molecule.
- Author
-
Xiao-Yin Pan and Sahni, Viraht
- Subjects
DENSITY functionals ,HYDROGEN ,MOLECULES ,IONIZATION (Atomic physics) ,QUANTUM chemistry ,DYNAMICS - Abstract
In this paper we perform a quantal density functional theory (Q-DFT) study of the hydrogen molecule in its ground state. In common with traditional Kohn–Sham density functional theory, Q-DFT transforms the interacting system as described by Schrödinger theory, to one of noninteracting fermions—the S system—such that the equivalent density, total energy, and ionization potential are obtained. The Q-DFT description of the S system is in terms of “classical” fields and their quantal sources that are quantum-mechanical expectations of Hermitian operators taken with respect to the interacting and S system wave functions. The sources, and hence the fields, are separately representative of all the many-body effects the S system must account for, viz. electron correlations due to the Pauli exclusion principle, Coulomb repulsion, and correlation-kinetic effects. The local electron-interaction potential energy of each model fermion is the work done to move it in the force of a conservative effective field that is the sum of the individual fields. The Hartree, Pauli, Coulomb, and correlation-kinetic energy components of the total energy are also expressed in virial form in terms of the corresponding fields. The highest occupied eigenvalue of the S system is the negative of the ionization potential energy. The Q-DFT analysis of the hydrogen molecule is performed employing the highly accurate correlated wave function of Kolos and Roothaan. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
40. Resonances in three-dimensional H+HLi scattering: A time-dependent wave packet dynamical study.
- Author
-
Padmanaban, R. and Mahapatra, S.
- Subjects
MESOMERISM ,SCATTERING (Physics) ,HYDROGEN ,LITHIUM ,POTENTIAL energy surfaces ,EIGENFUNCTIONS - Abstract
This paper examines the resonances in H+HLi scattering. The signature of these resonances is obtained from the oscillations in its reaction probability versus energy curves. They are identified here from a set of pseudospectra calculated for different initial locations of a stationary Gaussian wave packet on the ab initio potential energy surface (PES) reported by Dunne, Murrel, and Jemmer [Chem. Phys. Lett. 336, 1 (2001)]. The nuclear motion on this PES is monitored with the aid of a time-dependent wave packet method and the pseudospectrum are calculated by Fourier transforming the time autocorrelation function of the initial wave packet. The resonances are further examined and assigned by computing their eigenfunctions through spectral quantization algorithm. Both the linewidth as well as decay lifetimes of the resonances are reported. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
41. Ketene photodissociation in the wavelength range 193–215 nm: The H atom production channel.
- Author
-
Feltham, Emma J., Qadiri, Rafay H., Cottrill, Emily E.H., Cook, Phillip A., Cole, John P., Balint-Kurti, Gabriel G., and Ashfold, Michael N.R.
- Subjects
KETENES ,ANGULAR distribution (Nuclear physics) ,PHOTODISSOCIATION ,HYDROGEN - Abstract
The speed and angular distributions of H atom products arising in the photodissociation of jet-cooled ketene (CH[sub 2]CO) molecules following excitation at 193.3, 203.3, 209, and 213.3 nm have been investigated by H Rydberg atom photofragment translational spectroscopy. The observed product energy disposal is interpreted in terms of one photon absorption to the [sup 1]B[sub 1] electronically excited state, internal conversion to high lying vibrational levels of the ground state and subsequent unimolecular decay to yield the observed H (+HCCO) products. H atoms resulting from secondary photolysis of H containing primary products (most probably singlet CH[sub 2] radicals) are evident in the measured spectra, especially at high photolysis laser pulse energies. The kinetic energy distributions of the primary H+HCCO products span all energetically accessible product internal energies, peaking at ∼1170 cm-1 in the case of parent excitation at 213.3 nm, and rising to ∼1450 cm-1 (when exciting at 193.3 nm). These distributions are reproduced, qualitatively, by the statistical adiabatic product distribution (SAPD) method proposed recently by Cole and Balint-Kurti (J. Chem. Phys., preceding paper). This method is based on the use of a quantum mechanical, J conserving, Rice–Ramsperger–Kassel–Marcus (RRKM) treatment and provides a prediction of the product quantum state distributions and the total kinetic energy release spectra. Accurate, quadratic configuration interaction, intrinsic reaction coordinates have been computed for both the lowest singlet (S[sub 0]) and triplet (T[sub 1]) potential energy surfaces of CH[sub 2]CO. Quantum mechanical SAPD calculations have been performed using both surfaces; the results favor the conclusion that the dissociation occurs on the S[sub 0] surface. This conclusion is further supported by comparison of the calculated and previously measured CO product vibrational quantum state distributions arising from photodissociation at 193.3 nm. The variational RRKM method has also been used to compute the branching ratios for forming H+HCCO and CH[sub 2]+CO products on both the S[sub 0] and T[sub 1] surfaces. Different aspects of the SAPD model, such as the inclusion of quantum mechanical tunneling, the attractiveness of the long-range interfragment potential and the assumed adiabaticity of the fragmentation, have been varied in order to shed light on the nature of the dissociation process and the possible origins of the differences between the model calculations and the experimental results. It is found that the agreement between the quantum mechanical statistical model predictions and the experimentally observed total kinetic energy release spectra for the H atom dissociation channel can be greatly improved if the contribution of lower fragment relative orbital angular momenta is increased over that required by the use of a purely statistical model. This finding is equivalent to the conclusion that the dissociation is not entirely statistical, but that the dynamics of the break-up process plays some role. In particular the initial geometry of the parent molecule may restrict the body-fixed angles into which the final products can scatter and, through this, may restrict the relative orbital angular momenta to be on average smaller than that predicted by a purely statistical theory. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
42. Mechanism of H[sub 2] metabolism on Fe-only hydrogenases.
- Author
-
Liu, Zhi-Pan and Hu, P.
- Subjects
HYDROGEN ,HYDROGENASE - Abstract
The metabolism of hydrogen (H[SUB2]↔2H[SUP+]+2e[SUP-) constitutes a central process in the global biological energy cycle. Among all the enzymes that can mediate this process, Fe-only hydrogenases are unique in their particular high reactivity. Recently, some important progresses have been achieved. Following our previous paper [Z.-P. Liu and P. Hu, J. Am. Chem. Soc. 124, 5175 (2002)] that characterizes the individual redox state of the active site of Fe-only hydrogenase, in this work we have determined the feasible reaction pathways and energetics for the H[SUB2] metabolism on the active site of Fe-only hydrogenases, using density functional theory. We show that H[SUB2] metabolism possesses very low reaction barriers and a proximal base from a nearby protein plays an important role in H[SUB2] metabolism. [ABSTRACT FROM AUTHOR]
- Published
- 2002
- Full Text
- View/download PDF
43. Quantum dynamics of the D[sub 2]+OH reaction.
- Author
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Zhang, Dong H., Yang, Minghui, and Lee, Soo-Y.
- Subjects
QUANTUM theory ,POTENTIAL energy surfaces ,ELECTRONIC excitation ,HYDROGEN - Abstract
This paper presents fully converged integral cross sections for the D[sub 2](j[sub 1]=0,2,4)+OH(j[sub 2]=0,2,4)→HOD+D reaction on the YZCL2 potential energy surface. It is found that the influence of reagent rotation excitation on reactivity is relatively mild compared with that of the D[sub 2] vibration excitation, but is fairly important to the thermal rate constant at low temperature. In general, the OH rotation excitation tends to hinder the reaction, and the D[sub 2] rotation excitation tends to enhance the reactivity. The simultaneous reagent rotation has some correlated effect, with the influence of the D[sub 2] rotation excitation considerably dependent on the OH rotation excitation. It is also found that the reaction is strongly dependent on j[sub 12] (the coupled angular momentum between j[sub 1] and j[sub 2]), K[sub 0] (the projection of the reagent rotation on the body fixed axis), and the parity of the system, in particular for either the OH or D[sub 2] rotationally excited initial states, but this dependence becomes relatively weaker as the collision energy increases. Excellent agreement achieved between theory and experiment on the thermal rate coefficients for temperatures up to 400 K clearly shows that the YZCL2 potential energy surface is capable of producing “quantitatively” accurate results for the title reaction. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2002
- Full Text
- View/download PDF
44. Quantum mechanical study on energy dependence of probabilities of nonreactive vibrational...
- Author
-
Onda, Kunizo and Sakimoto, Kazuhiro
- Subjects
COLLISIONS (Nuclear physics) ,HELIUM ,HYDROGEN ,VIBRATIONAL spectra ,EXCHANGE reactions - Abstract
Studies a nonreactive vibrational transition, atom exchange reaction and dissociation processes in a collinear helium+hydrogen collision using a time-independent quantum mechanical method. Replacement to the algorithm based on three-point finite difference formula; Interaction potential surface; Energy dependence of probabilities.
- Published
- 1999
- Full Text
- View/download PDF
45. Chemical waves in the O2 + H2 reaction on a Rh(111) surface alloyed with nickel. II. Photoelectron spectroscopy and microscopy.
- Author
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Smolinsky, Tim, Homann, Mathias, von Boehn, Bernhard, Gregoratti, Luca, Amati, Matteo, Al-Hada, Mohamed, Sezen, Hikmet, and Imbihl, Ronald
- Subjects
CHEMICAL reactions ,RHODIUM ,OXYGEN ,HYDROGEN ,NICKEL ,PHASE separation ,MICROSCOPY ,PHOTOELECTRON spectroscopy - Abstract
Chemical waves in the H
2 + O2 reaction on a Rh(111) surface alloyed with Ni [ ΘNi < 1.5 monolayers (ML)] have been investigated in the 10-7 and 10-6 mbar range at T = 773 K using scanning photoelectron microscopy and x-ray photoelectron spectroscopy as in situ methods. The local intensity variations of the O 1s and the Ni 2p signal display an anticorrelated behavior. The coincidence of a high oxygen signal with a low Ni 2p intensity, which seemingly contradicts the chemical attraction between O and Ni, has been explained with a phase separation of the oxygen covered Rh(111)/Ni surface into a 3D-Ni oxide and into a Ni poor metallic phase. Macroscopic NiO islands (≈1 μm size) formed under reaction conditions have been identified as 2D-Ni oxide. Titration experiments of the oxygen covered Rh(111)/Ni surface with H2 demonstrated that the reactivity of oxygen is decreased by an order of magnitude through the addition of 0.6 ML Ni. An excitation mechanism is proposed in which the periodic formation and reduction of NiO modulate the catalytic activity. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
46. Chemical waves in the O2 + H2 reaction on a Rh(111) surface alloyed with nickel. I. Photoelectron emission microscopy.
- Author
-
Smolinsky, Tim, von Boehn, Bernhard, and Imbihl, Ronald
- Subjects
CHEMICAL reactions ,HYDROGEN ,OXYGEN ,RHODIUM ,NICKEL ,LOW energy electron diffraction ,AUGER electron spectroscopy ,PHOTOELECTRON spectroscopy - Abstract
Chemical waves that arise in the H
2 + O2 reaction on a bimetallic Rh(111)/Ni surface have been studied in the 10-6 and 10-5 mbar range at T = 773 K with photoelectron emission microscopy (PEEM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). Nickel coverages of 0.3, 0.6, and 1.0 monolayers were investigated. Coadsorbed with some oxygen, Ni starts to penetrate the Rh bulk region substantially only beyond 900 K. In the 10-5 mbar range, chemical waves are characterized by three distinct gray levels in PEEM. This number reduces to only two levels in the 10-6 mbar range. In situ LEED showed the periodic appearance of a (nx1) (n = 8, 10) pattern during chemical waves which was assigned to a 2D-Ni oxide. With in situ AES, one observes that the bright phase in PEEM correlates with a high Ni coverage and the dark phase with a low Ni coverage. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
47. Theoretical characterization of the potential energy surface for H+N2→HN2. II. Computed points to define a global potential.
- Author
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Walch, Stephen P.
- Subjects
- *
POTENTIAL energy surfaces , *HYDROGEN , *NITROGEN , *QUANTUM theory - Abstract
A previous calculation for H+N2 [Walch, Duchovic, and Rohlfing, J. Chem. Phys. 90, 3230 (1989)] focused on the minimum energy path (MEP) region of the potential energy surface and on estimates of the lifetime of the HN2 species. In this paper, we report energies computed at geometries selected to permit a global representation of the potential energy surface (PES). As in the previous work, the calculations were performed using the complete active space self-consistent field/externally contracted configuration interaction (CASSCF/CCI) method. The surface was characterized using the same basis set as in the previous paper except that an improved contraction of the H s basis is used. Calculations with a larger basis set were carried out along an approximate MEP obtained with the smaller basis set. The new PES exhibits a sharp curvature, which was not present in the previous calculations, and has a slightly narrower and smaller barrier to dissociation. Saddle points for H atom exchange via collinear and T-shaped HN2 complexes are also reported. [ABSTRACT FROM AUTHOR]
- Published
- 1990
- Full Text
- View/download PDF
48. Atom–diatom reactive scattering. II. H+H2 and its isotopomers, J=0.
- Author
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Webster, Frank and Light, J. C.
- Subjects
- *
ATOMS , *REACTIVITY (Chemistry) , *HYDROGEN , *DEUTERIUM - Abstract
The solution of the reactive scattering problem by R-matrix propagation requires a number of choices which may affect the numerical accuracy. Although the formal definitions and development were given in detail in the preceding paper, in this paper we give (a) the specific choices and numerical procedures followed in our calculation, (b) a discussion and evaluation of the stability of the calculation with respect to these choices, and (c) results for three dimensional J=0 reactive scattering of H3, H2D, and HD2 systems in the energy range from threshold to about 1.30 to 1.50 eV. [ABSTRACT FROM AUTHOR]
- Published
- 1989
- Full Text
- View/download PDF
49. Accurate modified configuration interaction single-centered calculations for H[sup +][sub 2].
- Author
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Kempe, J.A. and Goldman, S.P.
- Subjects
MOLECULAR dynamics ,HYDROGEN - Abstract
Introduces an accurate single centered method for molecular calculations based on modified configuration interaction with infinite angular expansions. Calculation of the ground state energy of the hydrogen ion; Simplicity of the calculation; Inclusion of th vibrational-rotational motion of the nuclei.
- Published
- 1998
- Full Text
- View/download PDF
50. Six dimensional quantum dynamics study for dissociative adsorption of H2 on Cu(111) surface.
- Author
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Dai, Jiqiong and Light, John C.
- Subjects
QUANTUM theory ,ADSORPTION (Chemistry) ,HYDROGEN ,DISSOCIATION (Chemistry) ,POTENTIAL energy surfaces ,ANGULAR momentum (Mechanics) - Abstract
In this letter we present preliminary results of full six dimensional quantum dynamics calculations for dissociative adsorption of a hydrogen molecule on a Cu(111) surface. We utilize the time-dependent wave-packet approach to simulate the dissociation process on a full dimensional LEPS potential energy surface which has incorporated the latest ab initio data [Hammer et al. Phys. Rev. Lett. 73, 1400 (1994)]. We use a novel partitioning of the angular momentum operator in the split-operator method so that a direct product DVR can be rigorously implemented. The most interesting observation in the present rigorous quantum dynamics study is the site-averaged effect, i.e., the averaged dissociation probability of the four dimensional calculations over the three symmetric impact sites strongly resembles the exact dissociation probability of the six dimensional calculations. In accord with the low dimensional calculations, initial vibrational excitation of H
2 effectively reduces the translational threshold energy. The rotational orientation effect observed in the four dimensional studies remains in the present full dimensional dynamics with the cartwheel orientation yielding dramatically lower dissociative efficiency than the energetically equivalent helicopter orientation. We focus on normal incident scattering. The diffractive scattering and more detailed results will be presented in a later paper.. [ABSTRACT FROM AUTHOR]- Published
- 1997
- Full Text
- View/download PDF
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