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Accurate calculation of the energies and widths of the resonances of HOCl--an important intermediate in the O(1D)HCl reactive system--poses a challenging benchmark for computational methods. The need for very large direct product basis sets, combined with an extremely high density of states, results in difficult convergence for iterative methods. A recent calculation of the highly excited OH stretch mode resonances using the filter diagonalization method, for example, required 462,000 basis functions, and 180,000 iterations. In contrast, using a combination of new methods, we are able to compute the same resonance states to higher accuracy with a basis less than half the size, using only a few hundred iterations-although the CPU cost per iteration is substantially greater. Similar performance enhancements are observed for calculations of the high-lying bound states, as reported in a previous paper [J. Theo. Comput. Chem. 2, 583 (2003)]., (Copyright 2004 American Institute of Physics)

This paper demonstrates the performance of our previously suggested property-energy consistent method on the example of the generation of effective basis sets, pecS-1 and pecS-2, suited for the calculation of hydrogen, carbon, nitrogen, and oxygen chemical shifts. The new basis sets were successfully approbated in the GIAO-DFT calculations of the chemical shifts of 35 molecules using six different functionals. The pecS-1 basis set demonstrated very good accuracy, which makes this small basis set an effective means for the large-scale computations. At the same time, the pecS-2 basis set also gave very accurate results, thus putting it on a par with the other commensurate basis sets suited for the chemical shifts calculations. [ABSTRACT FROM AUTHOR]

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]

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]

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]

In this paper we report transition frequencies and line strengths computed for H2O-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 H2O acts as proton acceptor, a state with significant amplitude near the T-shape secondary potential minimum at which H2O acts as proton donor is identified by examining many different probability density plots. [ABSTRACT FROM AUTHOR]

Chemical waves in the H2 + 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]

Chemical waves that arise in the H2 + 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]

HOCl is a closed shell system in its ground electronic state. In common with many molecules it is photodissociated to give open shell fragments. In this paper the photodissociation process HOCl(X 1A′)+hν→HOCl(2 1A′)→OH+Cl is investigated. A model is proposed to predict the OH product spin–orbit and Λ-doublet state distributions as well as the distribution of the Cl atom spin–orbit states. The model considers both the electronic structure of the system and the nuclear motion. Predictions are made not only of the individual fragment state distributions and of their dependence on total initial angular momentum and photon frequency, but also of the degree of correlation between the production of the different states of the two open shell fragments. The computed results agree with the available experiments, in particular the current theory is the first to agree with experimental findings in predicting a smoothly varying OH rotational state distribution. It is demonstrated that the model reproduces the frequency dependence of the absorption line shape as computed using more exact procedures. In the simple treatment presented here rotational transitions during the dissociation process are ignored, as is the detailed coupling of the electronic states in the asymptotic region. Some of the remaining disagreements between the current predictions and the experimental results are ascribed to these approximations in the model. It is hoped that the predictions of the correlated product state distributions will stimulate coincidence experiments on the photodissociation process. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This is the first of a series of papers in which we investigate the unimolecular dissociation of hydroperoxyl. Using the DMBE IV potential energy surface [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)], in the present study 726 bound states of HO2(X) up to the H+O2 dissociation threshold are calculated in an attempt to access the extent of the coupling between the modes of the system. The first approach involves an analysis of the nodal structure of the wave functions. While the wave functions for the lowest states are regular and assignable, the degree of mixing and complexity rapidly increases with energy. The wave functions close to the dissociation threshold are mostly irregular without any clear cut nodal structure and fill the entire coordinate space available. Nevertheless, a small number of regular states, that are associated with large excitation in the O2 stretching coordinate and no or only little excitation in the other modes, are found even at high energies. The second approach used to study the degree of intramolecular coupling is an analysis of the energy spectrum. The nearest neighbor level spacing distribution, which probes the short-range correlation, as well as the Σ2 and Δ3 statistics, which are sensitive to the long-range correlations in the spectrum, are investigated and compared to the distributions predicted for regular and irregular spectra. Both of these approaches indicate that the system is almost totally irregular with a Brody parameter of about 92%. In addition, the sum of states at a particular energy, which is extremely important in all statistical models for unimolecular dissociation, is approximately calculated from the volume of classical phase space and found to be in excellent agreement with the exact quantum mechanical result. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

State-to-state reaction probabilities have been calculated for the reaction O+H2(υ=0,J) →OH(υ′,J′)+H near threshold using the quasiclassical trajectory technique. In most cases the total classical angular momentum J of the system was held equal to zero. The procedure for ‘‘quantizing’’ the product vibrational energy is somewhat ambiguous, and two procedures were used. The results were compared with the quantal calculations of Chatfield et al. on the same system for J=0. Both the classical and quantal calculations give very state-specific product distributions. The agreement between the classical and quantal calculations is reasonably good, particularly for the classical procedure which conserves the total product internal energy during the quantization procedure. The agreement is worst for J=0. For the case J=14 we have also carried out a calculation for all J values (i.e., all impact parameters and initial orientations) of the product density distribution P(Evib′,Erot′) and compared it with the comparable distribution for J=0. Here, Evib′ and Erot′ are the product vibrational and rotational energies. The results for all J show a peaked product distribution, but it is broader than that for J=0 and it has a somewhat different correlation between Evib′ and Erot′. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Graphene-based derivatives with covalent functionalization and well-defined stoichiometry are highly desirable in viewof their application as functional surfaces. Here, we have evaluated by ab initio calculations the energy of formation and the phase diagram of hydroxylated graphane structures, i.e., fully functionalized graphene derivatives coordinated with -H and -OH groups. We compared these structures to different hydrogenated and non-hydrogenated graphene oxide derivatives, with high level of epoxide and hydroxyl groups functionalization. Based on our calculations, stable phases of hydroxylated graphane with lowand high contents of hydrogen are demonstrated for high oxygen and hydrogen partial pressure, respectively. Stable phases of graphene oxide with a mixed carbon hybridization are also found. Notably, the synthesis of hydroxylated graphane has been recently reported in the literature. [ABSTRACT FROM AUTHOR]

The purpose is to fit an accurate smooth function of the many-body expansion type to a multidimensional large data set using a basis-set type method. By adopting a combined-hyperbolic-inverse-power-representation for the basis, the novel approach is tested in detail for the ground electronic state of tri-hydrogen and hydroperoxyl systems, assuming that their potential energy surfaces are single-sheeted representable. It is also shown that the method can be easily applicable to potential energy curves by considering as prototypes molecular oxygen and the hydroxyl radical. [ABSTRACT FROM AUTHOR]

Using Fourier transform infrared spectroscopy, we have analyzed the time evolution of the ν2 mode of (oH2)n:H2O clusters (n=11 to 1) embedded in solid normal hydrogen at 4.2 K over a period of 150 h using paramagnetic O2 to speed up the ortho to para nuclear spin conversion process. For concentrations H2O/O2/H2=1/20/4000, at time t=0 right after the solid is prepared, all the H2O molecules are preferentially clustered by large numbers of oH2. With time the cluster distribution irreversibly shifts toward smaller cluster sizes and also generates freely rotating H2O (n=0) which is solvated completely by pH2 molecules. From a spectral decomposition of the ν2 (oH2)n:H2O cluster spectra, a phenomenological simulation of the time behavior of the clusters has been developed. The time evolution is modeled using coupled rate equations in a step by step n to n-1 cluster cascade fashion and analyzed over nine successive time periods. It shows that rotating H2O grows only at the expense of cluster n=1 and that the process dramatically slows down as the conversion of orthohydrogen proceeds. At the end of the conversion process, it was found that cluster n=1 remained with a very slow decrease. [ABSTRACT FROM AUTHOR]

The gas phase reaction of molecular oxygen and hydrogen catalyzed by a Au3 cluster to yield H2O2 was investigated theoretically using second order Z-averaged perturbation theory, with the final energies obtained with the fully size extensive completely renormalized CR-CC(2,3) coupled cluster theory. The proposed reaction mechanism is initiated by adsorption and activation of O2 on the Au3 cluster. Molecular hydrogen then binds to the Au3O2 global minimum without an energy barrier. The reaction between the activated oxygen and hydrogen molecules proceeds through formation of hydroperoxide (HO2) and a hydrogen atom, which subsequently react to form the product hydrogen peroxide. All reactants, intermediates, and product remain bound to the gold cluster throughout the course of the reaction. The steps in the proposed reaction mechanism have low activation energy barriers below 15 kcal/mol. The overall reaction is highly exothermic by ∼30 kcal/mol. [ABSTRACT FROM AUTHOR]

The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The interaction of gas-phase H atoms with ordered and disordered adlayers of atomic oxygen, hydroxyl, and molecular oxygen on Pt(111) surfaces was investigated by in situ mass spectrometry and post-reaction TPD (temperature programed desorption). Exposure of oxygen adlayers to gas-phase H atoms at 85 K leads to formation of H[sub 2]O via two consecutive hydrogenation reactions: H(g)+O(a)→OH(a) followed by H(g)+OH(a)→H[sub 2]O(g,a). Both reaction steps are highly exothermic, and nascent H[sub 2]O molecules partially escape into the gas phase before being thermally accommodated on the surface. Empty surface sites and hydrogen bonding promote thermalization of H[sub 2]O. Separate experiments performed with OH-covered Pt(111) surfaces reveal that the hydrogenation of hydroxyl is a slow reaction compared to the hydrogenation of atomic oxygen; additionally, the abstraction of H from OH by gas-phase D atoms, OH(a)+D(g)→O(a)+HD(g), was detected. Abstraction of H from adsorbed H[sub 2]O was not observed. Admission of gas-phase H atoms to O[sub 2]-covered Pt(111) surfaces at 85 K leads to the desorption of O[sub 2] and H[sub 2]O. The thermodynamic stability of the HO[sub 2] radical suggests that the reaction is initiated by hydrogenation of molecular oxygen, O[sub 2](a)+H(g)→HO[sub 2]. The intermediate HO[sub 2] either decomposes via dissociation of the HO–O bond, HO[sub 2]→OH(a)+O(a), finally leading to the formation of H[sub 2]O (∼85%), or via dissociation of the H–O[sub 2] bond thus leading to desorption of O[sub 2] (∼15%). The whole reaction sequence of formation and decomposition of HO[sub 2] is fast compared to the formation of H[sub 2]O via hydrogenation of atomic oxygen and hydroxyl. The observed coverage dependence of the reaction kinetics indicates the dominance of hot-atom mediated reactions. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the spectral response of the transition between the first and the second excited state of the O–H stretch vibration of HDO dissolved in liquid D[sub 2]O with two-color femtosecond mid-infrared spectroscopy. The spectral response of this transition differs strongly from the fundamental absorption spectrum of the O–H stretch vibration. In addition, excitation of the O–H stretch vibration is observed to lead to a change of the hydrogen-bond dynamics of liquid water. We show that both these observations can be described with a refined quantum-mechanical version of the Lippincott–Schroeder model for hydrogen-bonded OH...O systems. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the resonant ion stimulated desorption of oxygen and hydrogen. Mechanism of noncollisional sputtering of oxygen and proton; Diffusion/segregation of oxygentaion adatoms; Effect of ultraviolet (UV) photon irradiation.

Studies the effect of coadsorbed argon, hydrogen and oxygen on the internal vibration of CO on Ru(001) by infrared absorption spectroscopy in order to disentangle electrostatic and chemical frequency shifts; Intermolecular interactions among CO molecules avoided by working at very low CO coverages.

Calculates the fundamental and overtone oxygen-hydrogen stretching vibrational band intensities of the water dimer and trimer. Determination of intensities with a simple harmonically coupled anharmonic oscillator local mode model; Dipole moment functions calculated at the self-consistent-field Hartree-Fock.

The spectrum associated with the J=3←2 transition of OH+ in the a 1Δ(v=0) state has been observed by far infrared laser magnetic resonance spectroscopy. A new microwave discharge source enabled the detection of this spectrum, which is the first observation of the rotational spectrum of an ion in a metastable state. Assignment and least-squares fitting of the observed transitions have determined the following molecular constants: B0=494.420 388 (22) GHz, the proton hyperfine parameter a=74.84 (32) MHz, gL’ = 1.000 915 (15), and gr=-0.001 815 (18), with the 1σ uncertainties of the last digits in parentheses. The relationship of these parameters to the geometric and electronic structure of OH+ is discussed. [ABSTRACT FROM AUTHOR]

Rate constants for the isotope exchange reactions of OH- with D2 and OD- with H2 have been measured as a function of average center-of-mass kinetic energy at several temperatures. The reaction of OH- with D2 is slightly exothermic, and the rate constant has a negative temperature dependence. The kinetic energy dependences of the rate constants have minima near 0.1 eV. A strong negative dependence on the D2 rotational temperature was found. The reason for this dependence is unclear at present. In contrast, the reaction of OD- with H2 is slightly endothermic and shows positive dependences on both temperature and kinetic energy. The negative rotational dependence for the reaction of OD- with H2 is not as large as that for OH-+D2, presumably because rotational energy can help overcome the endothermicity in the case of OD-+H2. Vibrational energy is observed to promote reactivity in both reactions. [ABSTRACT FROM AUTHOR]

We have analyzed the molecular-dynamics (MD) trajectories for the oxygen and hydrogen atoms of liquid water, at six temperatures (from hot, T=361 K, to supercooled water, T=242 K); in the MD simulations the Nieser-Corongiu-Clementi ab initio potential has been used, since it yields reliable x-ray and neutron-diffraction data as well as infrared, Raman, and neutron-scattering spectra. Our analysis leads to two complementary models where we can consider each water as a solvated molecule (placed at the center of a solvation shell) or as a component of a cyclic polymer, a substructure of the hydrogen-bonded network. In the first solvation shell all water molecules are solvated with coordination values in the range 2–8. The most probable solvation number is four, at low temperature, and five at high temperature considering oxygen–oxygen pairs; however, the coordination number is four at all the temperatures if we consider oxygen–hydrogen pairs. The lifetime of the tetra coordinated complexes is the largest one and increases as temperature decreases. The computed population of cyclic polymers is highest for the pentameters in the studied temperature range, the second most probable cyclic structure is for hexamers. The average O–O distances in the liquid are temperature dependent and shorter than those in the gas phase, approaching ice values at low temperature (except for cyclic trimers, for which the O–O distance is nearly temperature independent). As a preliminary result, the lifetime of the polygons is estimated to be around 0.01 ps. [ABSTRACT FROM AUTHOR]

Inelastic scattering cross sections are reported within the infinite-order sudden (IOS) approximation for excitation of overall and internal rotation in CH3OH by collisions with He at an average energy of 500 cm-1, using a self-consistent field (SCF) plus damped dispersion interaction potential. The sudden approximation was used for the overall as well as the internal rotation, which was described using the zero-order internal axis method (IAM). The torsionally elastic cross sections are dominated by ΔK=0 transitions, followed by ΔK=±3. However, torsional excitation is significant only for K-changing collisions, particularly ΔK=±3. These latter cross sections approach zero as ρ (the ratio of the internal rotor moment of inertia to that of the entire molecule about its symmetry axis), approaches unity. Cross sections were also calculated for the high-barrier and zero-barrier limits to internal rotation. The high-barrier limit values are close to those for the actual barrier of 373 cm-1. The zero-barrier cross sections show strong propensities toward particular K→K’, which are quite sensitive to the value of ρ. These propensities are weaker in the actual barrier cross sections. The results also show a propensity for A±A± over A±A∓ in ΔK=0 transitions. [ABSTRACT FROM AUTHOR]

Rotational transitions in the O(3P)+H2 reaction and its isotopic variations are studied. Product rotational-state distributions are calculated using an independent-event approximation together with a simplified distorted-wave cross section for collinear-favored reactions, both of which have been proposed recently. The calculation quite well reproduces the product rotational distribution obtained by Schatz performing an accurate CSDW (coupled-state–distorted-wave) calculation. It is found that not only the coordinate transformation but also the rotationally inelastic half collisions play significant roles in determining the product distribution. The contributions of each mechanism depend strongly on the system; the first mechanism is much more important than the second one for the O+DH reaction, while the second mechanism dominates the O+HD reaction. The rotational rainbow feature in a half collision is found to appear in the product distribution. [ABSTRACT FROM AUTHOR]

The rate constant for the reaction of O+2 with CH4 has been measured as a function of average center-of-mass kinetic energy, , at several temperatures over the range 93–545 K. The rate constant decreases with increasing at low and increases at higher ; the position of the resulting minimum depends on temperature. We have observed small differences in the rate constants measured at the same total but at different temperatures in the low temperature regime (T≤300 K). These differences, i.e., decreasing rate constants with increasing temperature, are discussed in terms of the possibility of a rate constant which is dependent upon rotational energy. At higher temperatures, 430 and 545 K, we find that the rate constant is significantly larger than that measured at lower temperatures at a given . This enhanced reactivity is attributed to vibrational excitation in the CH4. From these data, we derive a rate constant for vibrationally excited CH4 (in the low frequency modes) that is approximately a factor of 20 greater than the rate constant for the ground vibrational state. The data disagree with an early study of this type at low temperature. The disagreement is discussed, and arguments are presented which indicate that the earlier data are in error at low temperature with an applied drift field. The use of these data for deriving effective reaction temperatures in other nonthermal experiments is also discussed. [ABSTRACT FROM AUTHOR]

A comprehensive theoretical investigation of vibrational excitation and vibronic charge transfer in the H++O2 collision at ECM=23 eV is reported. The calculations of differential and integral scattering observables are undertaken within both the quantal infinite order sudden (QIOS) and the vibronic semiclassical (VSC) approximations. They involve 2×15 vibronic expansions associated with the diabatic states determined by Grimbert et al. [Chem. Phys. 124, 187 (1988)] using a so-called effective model potential (EMP) method. A quadripartite comparison involving experimental data of Noll and Toennies [J. Chem. Phys. 85, 3313 (1986)], results of a QIOS treatment of Gianturco et al. [Phys. Rev. A 42, 3926 (1990)] based on DIM potentials and the present QIOS, and VSC results is presented. From the comparison of the theoretical and experimental results we find that the present calculations based on the EMP reproduce much better the experimental data than those based on the DIM potentials. Though differences are found between the present QIOS and VSC results, the experimental data do not help deciding between the two theories. The relative merits of the QIOS and VSC approaches are put forward and discussed. By scrutinizing intermediate results of lengthy calculations we have been able to bring out elementary models in them. Pure vibrational excitation is found to be a prominent process in this system and charge transfer substantially affects it. [ABSTRACT FROM AUTHOR]

A number of vibrational bands of the A 2Σ+X 2Π electronic spectrum of both ArOH and ArOD have been investigated by laser induced fluorescence with a high-resolution, pulsed laser system yielding linewidths ≲250 MHz in the UV. This spectrum not only displays completely resolved rotational structure, but also fine and hyperfine structure. The hyperfine constants and precise interatomic distances derived from the rotational constants provide a very interesting picture of the electronic and geometric structure of the complex. The bonding is incipiently chemical in the A state with clear evidence for at least some electronic reorganization between Ar and the open-shell OH radical in the complex. Conversely, the X state appears to be bound almost solely by physical van der Waals interactions characteristic of systems containing only closed-shell species. [ABSTRACT FROM AUTHOR]

A quantum mechanical method is described for calculating state-selected cross sections and rate constants for four-atom reactions of the general form AB+CD→ABC+D with nonlinear geometry. The method involves using hyperspherical coordinates to describe the BC and CD bonds, accounting for both the rotation of the AB molecule and the bending mode of the ABC molecule with a spherical harmonic basis set, holding the AB spectator bond length fixed and applying a version of the bending-corrected-rotating line approximation to treat the rotation of the CD molecule. The method is applied to the OH(j)+H2(v)→H2O(n,m)+H reaction, and its reverse reaction, where v and j are vibrational and rotational quantum numbers, and n and m label bending and local OH-stretching vibrational states of the H2O molecule. A modified potential energy surface based on a fit to ab initio data is used. Comparisons of the calculated cross sections are made with quasiclassical trajectory calculations. The effect of the bending and stretching modes of the H2O molecule on the reaction is examined in detail. The calculated rate constants for the OH+H2 reaction agree very well with experiment over the whole temperature range of 250–1050 K. [ABSTRACT FROM AUTHOR]

Canonical Van Vleck perturbation theory (CVPT) is used to investigate rotation–vibration mixing of highly excited vibrational states of SO2 and H2CO. For SO2 we find a nearly complete separation of the rotational and vibrational degrees of freedom, even for J=12 and Evib=11 000 cm-1. In contrast, for H2CO we observe extensive mixing between rotational and vibrational degrees of freedom at similar rotational excitation but with Evib=8000 cm-1. Although a-axis Coriolis coupling is pronounced, b- and c-axis Coriolis couplings play an important additional role in mixing states with different Ka quantum numbers. The implementation of CVPT, the choice of internal coordinates, and the convergence of the results are discussed in detail. [ABSTRACT FROM AUTHOR]

The excitation of rapidly predissociating v’=3 levels in the A 2Σ+ state of OH has recently been suggested as a means of avoiding collisional quenching corrections when performing laser-induced fluorescence (LIF) measurements in flames. We report measurements of predissociation rates of several rotational levels in v’=3, obtained from linewidths in optical–optical double-resonance (OODR) spectra. The magnitude of the observed predissociation rates places an upper limit on the pressures at which OH LIF can be considered ‘‘quench-free.’’ In addition, analysis of spectral line shapes suggests that rotational transfer can significantly affect LIF quantum yields at pressures of 1 atm and higher. We conclude that variations of the predissociation rate with rotational level in v’=3 must be included in determinations of rotational temperatures from LIF. [ABSTRACT FROM AUTHOR]

Resonances in the quasistable A 1A‘ state of trans HONO are probed through photodissociation experiments. The OH fragment ejected by HONO excited to specific –N[larger_closed_square]O stretching vibrational levels of the A state is probed by high-resolution sub-Doppler spectroscopy of the R2(1) (1,0) A 2Σ+–X 2Π transition. The Doppler profiles provide information on the vibrational state dependence of HONO’s subpicosecond fragmentation time and OH fragment’s kinetic energy. The latter is used to deduce NO sister fragment’s translational and vibrational energy content. These provide quantitative probes for (a) V→T ‘‘energy transfer’’ from the photoselected N[larger_closed_square]O vibrational coordinate to the recoil O–N coordinate and (b) N[larger_closed_square]O ‘‘vibrational relaxation’’ during dissociation. The present results and our previous measurements on the HONO A–X linewidths are discussed in terms of an excited-state potential energy surface in which (a) the –N[larger_closed_square]O coordinate is coupled to the reaction coordinate (O–N) and (b) there is a bottleneck in the exit channel. [ABSTRACT FROM AUTHOR]

The infrared vibrational OH stretching spectrum of isotopically isolated HDO molecules in liquid water has been calculated by ab initio methods at the MP2 level for a number of geometrical configurations taken from a Monte Carlo simulation. Each vibrating water molecule with its environment was described by a pentamer supermolecule, surrounded by a large number of point charges representing polarized water molecules. The anharmonic stretching potentials (MP2 force constants up to fifth order) for 40 uncoupled OH water vibrators were calculated. The average computed re distance found for liquid water is 0.01 Å longer than the free-water value. The frequencies were obtained by solving the one-dimensional Schrödinger equation variationally for each OH potential curve. Using the squared dipole moment derivatives, which vary by a factor of 7 over the frequency band, the density-of-states histograms were converted to intensities. The resulting computed average frequency downshift is ∼260 cm-1, compared to ∼310 cm-1 (experimental), with a bandwidth in good agreement with experiment. The remaining discrepancy between theoretical and experimental frequency shifts is to a large part due to the charge transfer within the water clusters. This charge transfer gives rise to an electrostatic field which, at the site of the vibrating H atom, counteracts the downshift induced by the other environmental effects. The agreement between experiment and theory is very satisfactory when this charge transfer effect is corrected for or when point-charge embedded heptamer clusters are considered. [ABSTRACT FROM AUTHOR]

O(2p3Pj) atoms produced from the reaction between H(1s2S) and O2(X3Σ-g) at collision energies (Ecoll) of 2.5 and 2.1 eV are detected by a resonance enhanced multiphoton ionization technique. From the Doppler profile measurements of O(3Pj), the average kinetic energy released to the products is estimated. The results suggest that the average fraction of the kinetic energy disposal at Ecoll =2.1 eV is larger than that at Ecoll =2.5 eV. The obtained branching ratios of O(3Pj) j=2, 1, and 0 at Ecoll =2.5 eV are (0.70±0.02), (0.21±0.02), and (0.09±0.02), and those at Ecoll =2.1 eV are (0.63±0.02), (0.25±0.04), and (0.12±0.02), respectively, with error bars of ±σ. The results suggest that the nonadiabatic couplings at the last stage of the reaction are important for the determination of the ratios. [ABSTRACT FROM AUTHOR]

We present a quasiclassical trajectory study of the OH+CO reaction using a potential surface that has been derived from ab initio calculations. Among quantities that have been studied are cross sections for reaction and for HOCO complex formation, cross sections associated with reaction from excited vibrational and rotational states, product energy partitioning and CO2 vibrational-state distributions, HOCO lifetime distributions, and thermal and state-resolved rate constants. We also present the results of Rice–Ramsberger–Kassel–Marcus (RRKM) calculations, using the same potential-energy surface, of HOCO lifetimes and of reactive and complex formation rate constants. The trajectory results indicate that the dominant mechanism for reaction involves complex formation at low energies. However, a direct reaction mechanism is responsible for half the reactive cross section at higher energies. This leads to a rate constant that is weakly temperature dependent at low temperatures, and becomes strongly temperature dependent at high temperature. Our trajectory results agree with measured rates over a wide range of temperatures, but the trajectory results at low temperatures are dominated by classical ‘‘leak’’ through zero-point barriers, so this agreement may be somewhat fortuitous.Rate constants for nonreactive processes such as OH(v=1) deactivation by CO that are controlled by the HOCO formation step are well above experiment (factor of 6), while rate constants for processes such as CO(v=1) reaction with OH that are controlled by decay of HOCO into H+CO2 are much closer (factor of 2). This suggests that the entrance channel barrier on our surface is too loose while the exit barrier is accurate. The error in the entrance channel barrier is studied using RRKM, and it is found to be due to an incorrect out-of-plane bend potential in the analytical surface used. Modifying the potential so that it is more consistent with ab... [ABSTRACT FROM AUTHOR]

We investigate final rotational state distributions following the decay of long-lived resonance states with k*=0, 1, and 2 quanta of internal bending excitation. The calculations are related to the photodissociation of HONO on the S1 electronic state surface, truncated to two degrees of freedom namely the HO–NO dissociation bond and the ONO bending angle. The decay of the k*=0 resonance yields a smooth Gaussian-type distribution, in very good agreement with recent measurements. The distributions following the decay of the excited bending states show a bimodal behavior with the main maxima at high rotational states. The final angular momentum distributions reflect the coordinate-dependence of the dissociation wave function in the region of the transition state, mediated by the dynamics in the exit channel when the wave packet slides down the steep potential slope. A qualitative interpretation of the rotational state distributions is provided by a simple classical model which applies the transition-state wave function as a weighting for trajectories starting on a line that separates the intermediate complex from the product channel. [ABSTRACT FROM AUTHOR]

A molecular beam spectrometer has been used to observe the hyperfine spectrum and determine the electric dipole moment of the KOH molecule. This EDM had never been measured previously, although theoretical calculations had been made. A refined line shape fitting procedure has helped make possible this determination from the molecular beam hyperfine spectrum. The value of the EDM, which we found for the ground vibrational state, is 7.415±0.002 debye. The hyperfine constants, including the potassium nuclear quadrupole, both spin–rotation interactions, and the tensor and scalar spin–spin interactions have been determined for several vibrational states. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rovibrational state distributions and Doppler widths of CO fragments formed from unimolecular dissociation of HFCO in its ground electronic state are measured by vacuum ultraviolet laser-induced fluorescence, following state-selective preparation of the molecule in a single quantum state in the energy region of 2000 to 3000 cm-1 above the dissociation threshold by stimulated emission pumping. CO fragments are rotationally hot and distributed over J≤15 to J=63 with distributions peaking at J=45 to 50 depending upon the initial HFCO dissociative state. Although CO rotational distributions are significantly different for different initial states, about 20% of the total available energy is released on average as rotational energy of CO for all three initial states studied. The yield of CO(v=1) fragments is determined to be about 10% and CO(v≥2) fragments are not observed. The average Doppler width of CO fragments is 0.85 cm-1, which indicates that ∼50% of the total available energy is released as translation. The CO product state distributions and Doppler widths may be rationalized using a modified impulsive model with the ab initio transition state geometry. The dependence of product state distributions on the initial HFCO quantum state may reflect incomplete intramolecular vibrational energy redistribution. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The energy surface of CaOH has been studied and an isomer of the form of HCaO with an electronic state of 2Σ+ symmetry has been found. It is linear with H–Ca and Ca–O bond lengths of 2.021 and 2.002 Å, respectively, at the CISD level with a basis set of triple-zeta plus double polarization quality. The overall electronic structure is largely ionic and can be described as H(1s2)Ca(4s0)O(2s22p2x2p2y2p1z) (H-Ca2+O-). The minimum on the energy surface is well defined and the harmonic vibrational frequencies have been calculated. The O–H bond length and stretching frequency and the bending frequency of CaOH have also been calculated and compared with experiment. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The translational energy distribution for the H2O product from the reaction of H2 and O2 on Rh(111) was measured as a function of surface temperature at two different oxygen coverages. The results are well represented by Maxwell–Boltzmann velocity distributions significantly cooler than the surface temperature. For [O]=0.2 monolayers (ML), the product H2O is slightly faster than for [O]=0.1 ML. The energy distributions are very close to those observed for the trapped and desorbed molecules when scattering low energy H2O molecular beams from the Rh(111). We also measured the angular dependence of the energy and intensity of the product H2O at Ts=650 K. The velocity distribution of the H2O product is independent of final angle, and the relative intensities are cosine distributed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using the technique of hydrogen and deuterium substitution, the structure of water in concentrated lithium chloride aqueous solutions (LiCl·6H2O) is explored for the liquid, supercooled liquid, and glass states. It is found that changes in structure between the glass and supercooled states are minor, but that a major change in water structure occurs as the supercooled liquid is heated above the temperature of peritexy of the penta-hydrate (Tp=207 K). In particular the 4.4 Å peak in the OO pair correlation function of pure water, which is normally viewed as indicating tetrahedral short range coordination in water, is absent in the LiCl solution at the same temperature, but reappears strongly in the glass and supercooled states. Corresponding changes occur in the HH and OH correlation functions. In addition, correlations appear to extend nearly twice as far in the glass and supercooled liquid, compared to the room temperature liquid. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A lumped model for H2/O2 oxidation in the oscillatory regime is constructed by using the approach of approximate constrained nonlinear lumping based on an algebraic method within nonlinear perturbation theory. The fast variables approach zero rapidly such that the lumped model is constructed within a slow manifold by setting the identified fast variables to zero. The model dimension is reduced from 7 to 4. The variables representing the concentrations of H2, O2, H2O, and H are explicitly kept unlumped. The lumped model accurately reproduces the main features of the original system, such as oscillatory periods and concentration profiles. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Accurate 3D quantum state-to-state reaction probabilities and collision lifetimes for the H+O2→OH+O combustion reaction for total angular momentum J=0 are reported. The reaction probabilities are dominated by resonances, many of which overlap. The total reaction probability is not enhanced by vibrational or rotational excitation of the reactants. The first accurate final state distributions are presented, and probability is found to spread out into all open product vibrational and rotational channels, with a rather strong tendency to produce highly excited product rotational states. The first calculated collision lifetimes are presented, and resonances with lifetimes of 1–10 ps are found at most energies. Whether the reaction behaves statistically is discussed, and future extensions needed are also discussed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present global ab initio potential energy surfaces for the three lowest energy 1A’, 3A‘, and 1A‘ surfaces of HNO. These surfaces are the lowest three states of the HNO and HON molecules, and they correlate to the ground electronic states of H+NO and O+NH. In addition, the 3A‘ surface correlates to the ground state of N+OH. The surfaces are based on approximately 800 ab initio calculations that were done using an internally contracted multireference configuration interaction calculation with a large basis set. The ab initio points were fit to a combination of Morse and spline functions in each of the three possible Jacobi coordinates, and the resulting splines were smoothly switched together, and combined with other functions to yield globally defined potentials. Properties of the HNO and HON minima and dissociation energies on these potentials are in good agreement with previous high quality calculations. The N+OH and O+NH reactions are found to have no barriers to formation of HON or HNO, respectively. Isomerization of HON to HNO involves barriers that are higher than the HON dissociation barrier on the singlet surfaces but not on the triplet surface. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a quasiclassical trajectory study of the collisions which occur on the 1A’, 3A‘, and 1A‘ potential surfaces of HNO using recently developed global potential surfaces that were derived from ab initio calculations. Each of these surfaces was assumed to be uncoupled from the other surfaces for the purposes of the calculations, and the appropriate statistical average of electronic states for each process was calculated. For N+OH and O+NH, we specifically studied reactive collisions which give H+NO as products, and we also studied the production of N+OH from O+NH. Overall rate constants calculated for either N+OH or O+NH are in good agreement with most experiments, and in addition, the product NO vibrational distribution from the N+OH reaction is in good correspondence with recent measurements, revealing modest excitation that is close to what would be expected from a statistical distribution. For O+NH, the calculated NO vibrational distributions are much hotter than statistical, in apparent disagreement with recent measurements. However, a careful analysis of limitations on the measurements due to spectral interference and to collisional relaxation indicates that it is not possible to say if theory and experiment are at odds for this reaction. We find a significant cross section for O+NH→N+OH on the 3A‘ surface (roughly 5% of the total reactive cross section, independent of energy), and this leads to rate constants at low temperatures that are orders of magnitude higher at low temperature than estimates made earlier based on H atom abstraction on the 5Π surface.The mechanism of this reaction is found to involve three steps: addition to form HNO, isomerization to HON, and dissociation to produce N+OH. We have also studied nonreactive vibrational and rotational excitation in H+NO collisions, and we obtain distributions that are somewhat closer to experiment than obtained in previous theoretical studies, although... [ABSTRACT FROM AUTHOR]

Ab initio energy calculations using the Mo\ller–Plesset perturbation theory up to fourth order with the 6-31G(D,P) basis set have been performed for the H5O2+ ion cluster with and without a hydrogen molecule attached to it. In agreement with experimental results, a C2 structure which gives rise to only two high O–H stretching frequencies is predicted to be the only minimum of the isolated ion, whereas when H2 is present, again only one minimum is found which can be roughly assigned to be of the Cs type. This structure is predicted to have four active O–H stretching frequencies, again in agreement with the experimental spectrum. [ABSTRACT FROM AUTHOR]

A quantum dynamics study of the O(1D) + H2(v = 0 - 2, j = 0) system has been carried out using the potential energy surfaces of Dobbyn and Knowles [Mol. Phys. 91, 1107 (1997)]. A time-independent quantum mechanical method based on hyperspherical coordinates is adopted for the dynamics calculations. Energy dependent cross section, probability, and rate coefficients are computed for the elastic, inelastic, and reactive channels over collision energies ranging from the ultracold to thermal regimes and for total angular momentum quantum number J = 0. The effect of initial vibrational excitation of the H2 molecule on vibrational and rotational populations of the OH product is investigated as a function of the collision energy. Comparison of results for vibrational levels v = 0 - 2 of H2 demonstrates that the vibrational excitation of H2 and its non-reactive relaxation pathway play a minor role in the overall collisional outcome of O(1D) and H2. It is also found that while the state-resolved product vibrational distributions are sensitive to the initial collision energy and H2 vibrational level, the product rotational distribution depicts an inverted population that is largely insensitive to initial conditions. Rate coefficients evaluated using a J-shifting approximation show reasonable agreement with available theoretical and experimental results suggesting that the J-shifting approximation may be used to evaluate the rate coefficients for O(1D) + H2 reaction. [ABSTRACT FROM AUTHOR]

We investigated spin-orbit-induced intersystem crossing effects in the title reaction by the time-dependent wave-packet method combined with an extended split operator scheme. We performed non-adiabatic calculations of the fine-structure-resolved cross section and adiabatic calculations of integral cross section. The calculations are based on the potential energy surfaces of 3A′ and the two degenerate 3A′′ states [S. Rogers, D. Wang, A. Kuppermann, and S. Walch, J. Phys. Chem. A 104, 2308 (2000)], together with the spin-orbit coupling matrix [B. Maiti and G. C. Schatz, J. Chem. Phys. 119, 12360 (2003)] and singlet 1A′ potential energy surface [J. Dobbyn and P. J. Knowles, Faraday Discuss. 110, 247 (1998)]. The results of the O(3P) + D2 are similar to those of the O(3P) + H2 reaction. The product spin state-resolved reaction cross section and the total reaction cross section both show that the adiabatic channel is dominant in all cases, and the non-adiabatic channels have cross sections of several orders of magnitude smaller than the adiabatic channels at high collision energy. Although the cross sections caused by the intersystem crossing effects in the O(3P) + D2 reaction are larger than those in the O(3P) + H2 reaction, the differences in non-adiabaticity between these two reaction systems are quite modest. Based on the results of the O(3P) + H2 reaction, we can predict that the influence of spin-orbit on the total reaction cross sections of the O(3P) + D2 reaction is also insignificant. However, these non-adiabatic effects can be reflected in the presence of some forward-scattering in the angular distribution for the OD product. [ABSTRACT FROM AUTHOR]

The outcomes following collisional quenching of electronically excited OH A 2Σ+ by O2 and CO are examined in a combined experimental and theoretical study. The atomic products from reactive quenching are probed using two-photon laser-induced fluorescence to obtain H-atom Doppler profiles, O (3PJ) atom fine structure distributions, and the relative yields of these products with H2, O2, and CO collision partners. The corresponding H-atom translational energy distributions are extracted for the H + O3 and H + CO2 product channels, in the latter case revealing that most of the available energy is funneled into internal excitation of CO2. The experimental product branching ratios show that the O-atom producing pathways are the dominant outcomes of quenching: the OH A 2Σ+ + O2 → O + HO2 channel accounts for 48(3)% of products and the OH A 2Σ+ + CO → O + HCO channel yields 76(5)% of products. In addition, quenching of OH A 2Σ+ by O2 generates H + O3 products [12(3)%] and returns OH to its ground X 2Π electronic state [40(1)%; L. P. Dempsey, T. D. Sechler, C. Murray, and M. I. Lester, J. Phys. Chem. A 113, 6851 (2009)]. Quenching of OH A 2Σ+ by CO also yields H + CO2 reaction products [26(5)%]; however, OH X 2Π (v″ = 0,1) products from nonreactive quenching are not observed. Theoretical studies characterize the properties of energy minimized conical intersections in four regions of strong nonadiabatic coupling accessible from the OH A 2Σ+ + CO asymptote. Three of these regions have the O-side of OH pointing toward CO, which lead to atomic H and vibrationally excited CO2 products and/or nonreactive quenching. In the fourth region, energy minimized points are located on a seam of conical intersection from the OH A 2Σ+ + CO asymptote to an energy minimized crossing with an extended OH bond length and the H-side of OH pointing toward CO in a bent configuration. This region, exoergic with respect to the reaction asymptote, is likely to be the origin of the dominant O + HCO product channel. [ABSTRACT FROM AUTHOR]