水在金属表面的氢键网络结构振动谱研究

用从头计算分子动力学模拟方法研究了水在Pt(111)表面上的吸附。总能优化和振动谱分析都表明，在这个表面上水以有序的分子态双层结构存在。这一结论和最近对水在Ru(0001)表面上吸附的计算结果相悖，但和已有的实验相符。此外，文章作者首次确定双层结构中存在两种不同的氢键形式。这两种氢键可以通过0H伸缩振动模的振动谱得到直接证实。     

Dynamic properties of hydrogen-bonded networks in supercritical water

Dynamic properties of supercritical water at temperatures between 573 and 773 K and densities between 0.49 and 0.83 g/cm(3) have been investigated by molecular dynamics simulation and compared to states located on the vapor-liquid coexistence curve. A flexible simple point charge potential has been assumed for interactions in the subcritical states, whereas a reparameterization of that model has been performed to model the supercritical states. The hydrogen bonding structure and the diffusion coefficients in an ensemble of simulated states were previously analyzed and a good agreement with available experimental data was found. Dynamic properties of hydrogen bonding like the bond lifetimes and the influence of hydrogen bonds in the vibrational spectra are discussed along a range of simulation conditions. A nonlinear behavior of the hydrogen-bond lifetime as a function of temperature is observed in subcritical water whereas a linear dependence is found in supercritical water. Special attention is paid to the intermolecular vibrational spectrum (10-400 cm(-1)). It has been observed that the mode centered at 200 cm(-1), attributed to the intermolecular O-O stretching vibration in the ambient state remains active in the supercritical states.     

Vibrational response of hydrogen-bonded interfacial water is dominated by intramolecular coupling

Using the surface-specific vibrational technique of vibrational sum-frequency generation, we reveal that the double-peaked structure in the vibrational spectrum of hydrogen-bonded interfacial water molecules originates from vibrational coupling between the stretch and bending overtone, rather than from structural effects. This is demonstrated by isotopic dilution experiments, which reveal a smooth transition from two peaks to one peak, as D2O is converted into HDO. Our results show that the water interface is structurally more homogeneous than previously thought.     

Vibrational damping of adsorbed molecules: Effects of a realistic metal surface

The damping of a vibrationally excited CO molecule adsorbed on copper can be fully accounted for within an image-dipole interaction provided the effects of nonlocality and particularly a smooth electron density profile of the metal are taken into account.     

On the structure of a water molecule chemisorbed on a metal surface

A model using the electrostatic image force and the harmonic restoring force has been adapted to find the equilibrium structure of a chemisorbed water molecule on a metal surface. An estimate of the maximum possible increase in the HOH interbond angle upon chemisorption due to image forces is given.     

Dynamics of hydrogen-bonded water networks under high pressure: Neutron scattering and computer simulation

Abstract

Molecular dynamics simulation of proton-ordered high pressure ice modifications II and IX was performed. Dynamics of both isotope varieties, H₂O and D₂O, was simulated. Rectangular simulation box of ice II contained 576 and that of ice IX 768 molecules. The average kinetic energy corresponded to 82 and 201 K for ice II and to 87 and 203 K for ice IX. One-phonon densities of states were calculated via Fourier transformation of velocity autocorrelation functions and compared with those found experimentally from inelastic incoherent neutron scattering. This characteristic was calculated for all the molecules, as well as for the molecules of a particular crystallographic type. Both simulated ice modifications contain molecules of two different structural types. Dynamic characteristics of molecules of different types are slightly different. Splitting of the librational peak at about 60–70meV observed in the ice II experimental spectrum is mainly due to such difference. In the case of ice II simulated spectra reproduce experimental ones quite reasonably in the whole range of energies, while in the case of ice IX agreement with the experiment is worse.     

Vibrational spectrum at a water surface: a hybrid quantum mechanics/molecular mechanics molecular dynamics approach

A hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulation is applied to the calculation of surface orientational structure and vibrational spectrum (second-order nonlinear susceptibility) at the vapor/water interface for the first time. The surface orientational structure of the QM water molecules is consistent with the previous MD studies, and the calculated susceptibility reproduces the experimentally reported one, supporting the previous results using the classical force field MD simulation. The present QM/MM MD simulation also demonstrates that the positive sign of the imaginary part of the second-order nonlinear susceptibility at the lower hydrogen bonding OH frequency region originates not from individual molecular orientational structure, but from cooperative electronic structure through the hydrogen bonding network.     

Tailoring the structure of water at a metal surface: a structural analysis of the water bilayer formed on an alloy template

Recent studies show that structures based on the traditional "icelike" water bilayer are not stable on flat transition metal surfaces and, instead, more complex wetting layers are formed. Here we show that an ordered bilayer can be formed on a SnPt(111) alloy template and determine the structure of the water layer by low energy electron diffraction. Close agreement is found between experiment and the structure calculated by density functional theory. Corrugation of the alloy surface allows only alternate water molecules to chemisorb, stabilizing the H-down water bilayer by reducing the metal-hydrogen repulsion compared to a flat surface.     

Comments on chemisorption at a metal surface

The effect of the gradient correction to the exchange and correlation energies on chemisorption properties is examined using the evaluation of B_χc arrived at by Rasolt and Geldart. Quantities common to the study of hydrogen and alkali chemisorption on a high density metal are calculated for various forms of the energy functional within the linear response approach. It is found that the gradient correction is a quantitatively significant term, lowering binding energies by ≈ 10% and increasing the dipole sizably.     

Vibrational spectra of a plasma-polymerized coating on the surface of a silicon single crystal

The composition and structure of plasma-polymerized coatings on the surface of a silicon single crystal are studied using methods of mass spectrometry and vibrational spectroscopy. It is established that the coating on the side of the surface is a set of ordered and unordered regions of branched chains of halogenocarbons and halogenohydrocarbons. A significant thickness of the coating-substrate transition layer contains silicon carbide and nitrogen dissolved in carbon. A great bulk of the coating is made up of amorphous carbon. The coating mass contains adsorbed gases that block reactive centers. Consideration is given to the special features of recording of vibrational spectra, the coating structure, its differences over the depth, the structural difference between the coating and a polymer film, and aging of the polymer material. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 338–344, May–June, 1999.     

Vibrational states of metal complexes of protoporphyrin IX

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 137–144, March–April, 1995.     

Photodetachment of H-near a metal surface

By using the closed orbit theory, the photodetachment cross section of H^- near a metal surface is derived and calculated. The results show that the metal surface has great influence on the photodetachment process. As the ion-surface distance is very large, the influence of the electrostatic image potential caused by the metal surface becomes small and can be neglected. The period, action, and length of the detached electron＇s closed orbit are nearly the same as the case of the photodetachment of H^- near an elastic interface. However, with the decrease of the ion-surface distance, the influence of the metal surface becomes significant. The amplitude of the oscillation in the photodetachment cross section becomes complicated. Each resonance peak in the Fourier transformed cross section is associated with one electron＇s closed orbit. Unlike the case of the photodetachment of H^- near an elastic interface, the length of the closed orbit does not equal the twice distance between the ion and the surface. But with the increase of the ion-surface distance, the length of the closed orbit approaches the case of the closed orbit near an elastic interface, which suggests the correctness of our method. This study provides a new understanding on the photodetachment process of H^- in the presence of a metal surface.     

Vibrational spectra of water in solutions

On the basis of results obtained by the method of theoretical modeling, the spectra of water in solutions are interpreted as the sums of the spectra of water molecules associated with one and two molecules of the solvent. The concentration, isotopic, and temperature variations of the spectra investigated fully confirm the proposed interpretation.