Showing papers by "John C. Tully published in 1993"
TL;DR: In this article, a simulation of vibrational relaxation rates for a carbon monoxide molecule adsorbed on the (100) face of copper was performed using a self-consistently incorporating both phonon and nonadiabatic electronhole (e•h) pair mechanisms of energy dissipation.
Abstract: Stochastic dynamics simulations of vibrational relaxation rates are reported for a carbon monoxide molecule adsorbed on the (100) face of copper. A recently developed ‘‘molecular dynamics with electronic friction’’ scheme that self‐consistently incorporates both phonon and nonadiabatic electron–hole (e‐h) pair mechanisms of energy dissipation is employed. Lifetimes of the C–O stretch, the CO‐surface stretch, the frustrated rotation, and the frustrated in‐plane translation are examined as a function of temperature between 0 and 450 K. e‐h pair dissipation plays a significant role for all modes above 150 K. For the C–O internal stretching mode, the e‐h pair mechanism dominates and the lifetime depends weakly on temperature. The frustrated rotational (bending) mode is calculated to have the shortest lifetime at all temperatures, and the temperature dependence is weak. The e‐h pair contribution is again largest although the phonon contribution is significant. The CO‐surface stretch and the frustrated in‐plane...
166 citations
TL;DR: In this paper, the effect of electric fields of electrochemical strength on the vibrational relaxation of CO on Cu(100) was studied by first principles molecular orbital calculations on cluster models.
86 citations
TL;DR: In this paper, the present level of infrared spectroscopy at surfaces is described by using hydrogen-terminated silicon surfaces as model systems, and a special emphasis is given to the recent discovery of chemical etching to prepare Hterminated Si(111) surfaces because it has greatly helped in understanding structural and dynamical properties of H terminated silicon surfaces.
Abstract: In this review, the present level of infrared spectroscopy at surfaces is described by using hydrogen-terminated silicon surfaces as model systems. The electronic structure of the adsorbate, H, and the large mass difference between H and Si simplify the interpretation of the data and make it possible for the theories to give reliable quantitative information. In particular, ab initio cluster calculations provide an accurate structural description and precise vibrational frequencies for various surface configurations, and are used as the basis of a priori simulations of the line shape of H on silicon. A special emphasis is given to the recent discovery of chemical etching to prepare H-terminated silicon surfaces because it has greatly helped in understanding structural and dynamical properties of H-terminated silicon surfaces. In particular, both the energy and phase relaxation of the Si-H stretching vibration on the flat, ideally hydrogen terminated Si(111) surface have been measured directly and evidence for vibrational energy diffusion has been obtained on vicinal, H-terminated Si(111) surfaces. The data and current theoretical understanding of the chemically prepared Si(111) surfaces are presented and discussed.
60 citations
01 Jan 1993
TL;DR: In this paper, the preparation and characterization of A x C 60 (A = alkali metal, x = 2,3,4,6) by powder X-ray diffraction, NMR (13 C, 23 Na and 87 Rb), and d.c. magnetization are reported.
Abstract: Alkali metal fullerides (A x C 60 ) are a subject of considerable current interest because of the occurrence of superconductivity for A x C 60 at temperatures surpassed only by the high T c copper oxides. The preparation and characterization of A x C 60 (A = alkali metal, x = 2,3,4,6) by powder X-ray diffraction, NMR ( 13 C, 23 Na and 87 Rb), and d.c. magnetization are reported. The structures are described as intercalation compounds of the FCC structure of pristine c 60 or of hypothetical BCC or BCT structures. The structures and phase diagrams can be rationalized on the basis of ion size and electrostatic considerations. Only the A 3 C 60 compounds are metallic (and superconducting). The superconducting T c increases nearly linearly with unit cell size. EHT (Extended Huckel Theory) calculations and 13 C NMR relaxation measurements indicate higher densities of states for the higher T c compositions.
4 citations
TL;DR: In this article, the preparation and characterization of A x C 60 (A = alkali metal, x = 2,3,4,6) by powder X-ray diffraction, NMR (13 C, 23 Na and 87 Rb), and d.c. magnetization are reported.
Abstract: Alkali metal fullerides (A x C 60 ) are a subject of considerable current interest because of the occurrence of superconductivity for A x C 60 at temperatures surpassed only by the high T c copper oxides. The preparation and characterization of A x C 60 (A = alkali metal, x = 2,3,4,6) by powder X-ray diffraction, NMR ( 13 C, 23 Na and 87 Rb), and d.c. magnetization are reported. The structures are described as intercalation compounds of the FCC structure of pristine c 60 or of hypothetical BCC or BCT structures. The structures and phase diagrams can be rationalized on the basis of ion size and electrostatic considerations. Only the A 3 C 60 compounds are metallic (and superconducting). The superconducting T c increases nearly linearly with unit cell size. EHT (Extended Huckel Theory) calculations and 13 C NMR relaxation measurements indicate higher densities of states for the higher T c compositions.