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Metal–water interfaces are central to many electrochemical, (electro)catalytic, and materials science processes and systems. However, our current understanding of their thermodynamic properties is limited by the scarcity of accurate experimental and computational data and procedures. In this work, thermodynamic quantities for metal–water interface formation are computed for a range of FCC(111) surfaces (Pd, Pt, Au, Ag, Rh, and PdAu) through extensive density functional theory based molecular dynamics and the two-phase entropy model. We show that metal–water interface formation is thermodynamically favorable and that most metal surfaces studied in this work are completely wettable, i.e., have contact angles of zero. Interfacial water has higher entropy than bulk water due to the increased population of low-frequency translational modes. The entropic contributions also correlate with the orientational water density, and the highest solvation entropies are observed for interfaces with a moderately ordered first water layer; the entropic contributions account for up to ∼25% of the formation free energy. Water adsorption energy correlates with the water orientation and structure and is found to be a good descriptor of the internal energy part of the interface formation free energy, but it alone cannot satisfactorily explain the interfacial thermodynamics; the interface formation is driven by the competition between energetic and entropic contributions. The obtained results and insight can be used to develop, parameterize, and benchmark theoretical and computational methods for studying metal–water interfaces. Overall, our study yields benchmark-quality data and fundamental insight into the thermodynamic forces driving metal–water interface formation. [ABSTRACT FROM AUTHOR]

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Straining of the Cu nanorod influences CO2 adsorption energy but does not change the preferred nanorod position on zirconia. Altogether, our results highlight that CO2 adsorption and activation depend sensitively on the chemical composition and atomic structure of the interface used in the calculations. This structure sensitivity may potentially impact further catalytic steps and the overall computed reactivity profile. [ABSTRACT FROM AUTHOR]

Numerical wave packet simulations are performed for studying coherent anti-Stokes Raman scattering (CARS) for CN radicals. Electronic coherence is created by femtosecond laser pulses between the X 2Σ and B 2Σ states. Due to the large energy separation of vibrational states, the wave packets are superpositions of rotational states only. This allows for a specially detailed inspection of the second- and third-order coherences by a two-dimensional imaging approach. We present the time-frequency domain images to illustrate the intra- and intermolecular interferences, and discuss the procedure to rationally control and experimentally detect the interferograms in solid Xe environment. [ABSTRACT FROM AUTHOR]

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH3) in a solid krypton matrix at 17–31 K temperature range. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm excimer laser radiation during the krypton gas condensation on the substrate. The ESR spectrum exhibits only isotropic features at the temperature range examined, and the intensity ratio between the symmetric (A) and antisymmetric (E) spin state lines exhibits weaker temperature dependence than in a solid argon matrix. However, the general appearance of the methyl radical spectrum depends strongly on temperature due to the pronounced temperature dependency of the E state linewidths. The rotational energy level populations are analyzed based on the static crystal field model, pseudorotating cage model, and quantum chemical calculations for an axially symmetric, planar rotor. Crystal field strength parameter values of -140 cm-1 in Ar and -240 cm-1 in Kr match most closely the experimentally observed rotational energy level shifts from the gas phase value. In the alternative model, considering the lattice atom movement in a pseudorotating cage, the effective lowering of the rotational constants B and C to 80%–90% leads to similar effects. [ABSTRACT FROM AUTHOR]

The authors report adaptive resolution molecular dynamics simulations of a flexible linear polymer in solution. The solvent, i.e., a liquid of tetrahedral molecules, is represented within a certain radius from the polymer’s center of mass with a high level of detail, while a lower coarse-grained resolution is used for the more distant solvent. The high resolution sphere moves with the polymer and freely exchanges molecules with the low resolution region through a transition regime. The solvent molecules change their resolution and number of degrees of freedom on the fly. The authors show that their approach correctly reproduces the static and dynamic properties of the polymer chain and surrounding solvent. [ABSTRACT FROM AUTHOR]

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH3) in a solid argon matrix at 14–35 K temperatures. The radicals were produced by dissociating methane by plasma bursts generated either by a focused 193 nm laser radiation or a radio frequency discharge device during the gas condensation on the substrate. The ESR spectrum exhibits axial symmetry at the lowest temperature and is ascribed to ground state molecules with symmetric total nuclear spin function I=3/2. The hyperfine anisotropy (A∥-A⊥) was found to be -0.01 mT, whereas that of the g value was 2.5×10-5. The anisotropy is observed for the first time in Ar and is manifested by the splitting of the low-field transition. Elevation of temperature leads reversibly to the appearance of excited state contribution having antisymmetric I=1/2. As a function of the sample temperature, the relative intensities of symmetric and antisymmetric spin states corresponding to ground and excited rotor states, respectively, proton hyperfine and electron g-tensor components, and spin-lattice relaxation rates were determined by a numerical fitting procedure. The experimental observations were interpreted in terms of a free rotation about the C3 axis and a thermal activation of the C2-type rotations above 15 K. The ground and excited rotational state energy levels were found to be separated by 11.2 cm-1 and to exhibit significantly different spin-lattice coupling. A crystal field model has been applied to evaluate the energy levels of the hindered rotor in the matrix, and crystal field parameter ε4=-200 cm-1, corresponding to a 60 cm-1 effective potential barrier for rotation of the C3 axis, was obtained. [ABSTRACT FROM AUTHOR]

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the “free” and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2–Xe complex. The harmonic frequency of the I2–Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase. [ABSTRACT FROM AUTHOR]

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadiabatic dynamics, or long with respect to period of molecular libration, which leads to synchronous alignment due to nearly adiabatic following. The results are contrasted to existing gas phase studies. In particular, the irregularity of the crystal-field energies leads to persistent interference patterns in the alignment signals. The use of nonadiabatic alignment for interrogation of crystal-field energetics and the use of adiabatic alignment for directional control of molecular dynamics in solids are proposed as practical applications. [ABSTRACT FROM AUTHOR]

The formation of iodine clusters in a solid krypton matrix is analyzed by using resonance Raman spectroscopy. The larger, bulklike shift has appeared when the iodine molecule is coordinated from two opposite directions as in the case of a pentamer and higher clusters and the structural motif of crystalline iodine is recognized in the clusters, starting from the pentamer.

Infrared and Raman spectroscopy are used for studying the structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature. The studies have shown that the [I.sub.2]-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes.

Reports on ab initio and molecular dynamics studies on rare gas hydrides. Potential energy curves; Isotropic hyperfine properties; Matrix cage trapping of atomic hydrogen; Derivation of classical trajectories for nuclear motion in a lattice with a single hydrogen atom.

Studies the thermal mobility of atomic hydrogen in solid argon and krypton matrices. Photodissociation of HBr achieved in an Ar matrix; Krypton matrix; Geminate recombination of photofragments in homogeneous conditions.

Potential energy curves for 13 lowest electronic states of S[sub 2] and 6 lowest states of ArS are computed at the MRCI level utilizing the CASSCF orbitals. The electronic structure of S[sub 2] is described by the correlation consistent cc-pVQZ basis set, whereas for ArS the augmented version of this basis is combined with ten electron-core pseudopotential basis set for S and Ar, respectively. Thermal and shock wave induced recombination dynamics of sulfur atoms trapped in Ar lattice are investigated by classical Molecular Dynamics simulations. It is observed that atoms separated by nearest neighbor distance of the lattice do immediately recombine even at 1 K with no thermal activation. While separated by one lattice constant, the S atoms stay stable up to 80 K and no recombination is observed in the classical trajectories. Consequently, the simulation was able to reproduce the experimental S+S glow curve only by lowering the reaction barrier by introducing lattice vacancies in the four atom plane separating the S-S pair. Local 1.1 eV kinetic excitation of a lattice atom next to the trapped S-S pair or artificial shock waves initiated by more distant excitation at 2 eV or more greatly enhanced the probability for recombination. Nonradiative [sup 1]D-[sup 3]P relaxation of sulfur provides a mechanism for such phonon emission and is discussed as a potential reason for the observed photoinduced recombination in low temperature Ar matrix. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

CO 2 adsorption and activation on a catalyst are key elementary steps for CO 2 conversion to various valuable products. In the present computational study, we screened different Cu-ZrO 2 interface structures and analyzed the influence of the interface structure on CO 2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO 2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO 2 prefers a bent bidentate configuration at the Cu-ZrO 2 interface and the molecule is clearly activated being negatively charged. Straining of the Cu nanorod influences CO 2 adsorption energy but does not change the preferred nanorod position on zirconia. Altogether, our results highlight that CO 2 adsorption and activation depend sensitively on the chemical composition and atomic structure of the interface used in the calculations. This structure sensitivity may potentially impact further catalytic steps and the overall computed reactivity profile.

The properties of the 1:1 iodine-benzene complex isolated in a solid Kr matrix at low temperatures have been studied using UV-vis absorption, FTIR, resonance Raman, and femtosecond coherent anti-Stokes Raman spectroscopy (fs-CARS). The use of all these techniques on similar samples provides a wide view on the spectroscopic properties of the complex and allows comparison and combination of the results from different methods. The results for the complex cover its structure, the changes in the iodine molecule's vibrational frequencies and electronic absorption spectrum upon complexation, and the dynamics of the complexed I(2) molecule on both ground and excited electronic states. In addition, polarization beats between uncomplexed benzene and iodine molecules are detected in the fs-CARS spectra, showing an amplification of an electronically nonresonant CARS signal by the resonant iodine signal. The possibility of controlling the charge-transfer reaction of the I(2)-Bz complex using the excitation of a well-defined ground-state vibrational wavepacket, according to the Tannor-Rice-Kosloff scheme, is discussed on the basis of the experimental findings.