Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools.

The surface properties of rare gas crystals have been explored using a He molecular beam as the dynamical probe. Specifically, ordered monolayer, bilayer, trilayer, and bulk Ar, Kr, and Xe were grown on an Ag(111) substrate). This has allowed us to examine how the physical properties of these films evolve on a layer by layer basis. Elastic diffraction and selective adsorption experiments were used to investigate the He-surface interaction potential. Comparing the results of close-coupled calculations with the experimental data, both the laterally averaged potential and higher order terms in the energy expansion can be determined. To examine the dynamical properties of the adsorbed rare gases, angle and time resolved inelastic scattering was used. This technique made it possible to investigate the dynamics of the surface across the entire Brillouin zone. In this paper on the properties of Ar(111) multilayers are specifically examined. These data are compared to the theoretical calculations of several other groups, testing the validity of several model potentials, and the importance of various interaction terms when constructing these potentials. Originator supplied keywords include: Surface phonon spectroscopy; phonon dispersion curves; surface dynamics; thin films; inelastic single phonon scattering; physisorption interactions; gas-surface energy exchange; rare gas interaction potentials.

Research involving the chemical physics of the inert or rare gases continues unabated. This small volume is meant to deal with advances that have occurred in three selected areas over the past decade. It forms a natural outgrowth of earlier reviews and volumes that have dealt almost exclusively with pure rare-gas solids. Originally, a single chapter was envisaged to cover the topic of alloys and impurities in solid rare gases. However, over the past ten years this single chapter spawned many offshoots and eventually the project became too large for a single volume. Thus the present book contains only a small subset of possbile topics involving rare-gas solids intentionally doped with impurities. Chapter 1 gives a brief overview of current research devoted to the rare gases. This is followed by a comprehensive, self-contained chapter dealing with the most recent developments in the area of interatomic inter actions. Chapter 3 is concerned with the lattice dynamics of rare-gas solids doped with an impurity which is either another rare-gas or a small molecule. The final chapter deals with the spectroscopy of vibrating and rotating di atomic impurities in rare-gas solids. The birth of this volume was not without its labour pains. I should like to take this opportunity to thank the various people who have at one time or another been involved throughout its gestation period. Clearly, many important topics are omitted from this volume.

A series of hyperthermal energy, ion/surface scattering experiments were performed. These studies examined and characterized some of the many processes occurring in energetic gas/surface collisions. In the scattering of Ne+ on Si(001), the precise amount of momentum, transferred to the surface upon collision, was measured under various conditions. Models that incorporate image charge interactions and inelastic energy loss were successfully applied to simulate the data. The first measurement of atom abstraction at an oxide surface was recorded in the scattering of NO+ on O/Al(111). Measurement of the product yield and energy distribution as a function of incident energy revealed the detailed reaction mechanism. The growth and erosion of SiO2 thin films under O+ bombardment was studied. Isotopic labeling experiments combined with mass-, energy-, and angular-resolved detection provided compelling evidence for a direct Eley-Rideal abstraction of adsorbed oxygen by incident O+ ions. This reaction pathway competes directly with sputtering channels in the formation of scattered O2- and SiO+. The conclusions from this work help in the modeling of spacecraft interactions with the LEO environment, e.g., vehicle drag, spacecraft charging, oxidation/degradation of exposed surfaces, and the formation of signatures.

Dynamics of Gas-Surface Scattering ...