Research directed toward understanding the dynamical factors governing the adsorption of molecules typically involved in heterogeneous catalytic processes has been continued at Harvard. Adsorption is the first step in any catalytic process, and predictions of rates of adsorption are fundamental to calculations of rates of catalytic reactions. Often activation of the bonds within the molecule proceed via a molecular precursor, and the rate of activation is determined by competitive bond activation and desorption of this precursor. Thus predictive capabilities for the adsorption probabilities of hydrocarbons become important for understanding the rates of simple reactions involving alkanes, such as reforming. In this work we have focused on the dynamics of molecular adsorption of low molecular weight alkanes on single crystal surfaces of platinum group metals in order to understand how different physical properties of the metals affect different trapping (adsorption) probabilities of the alkanes. The overall objective of these studies was to make a quantitative comparison of the molecular probabilities of C2-C4 alkanes on different metals in order to assess the effects of the structures of the different alkanes and the intrinsic differences of the metals on the reactivity of the alkanes. This work built on previous studies with platinum and palladium single crystal surfaces for which we were able to apply molecular dynamic simulations to quantitatively predict trapping probabilities of low molecular weight alkanes for palladium directly from measured values of the trapping of ethane (only) on Pt(111). The trapping probabilities for the alkanes are higher on Pd(111) due to a larger dissipation of energy to lattice vibrations upon collision, suggesting a general scaling of trapping with the lattice force constant for different metal surfaces, provided the surface structure is not too different. In this grant period we have thus focused on the dynamics of molecular adsorption of low molecular weight alkanes on single crystal surfaces of platinum, palladium, copper, silver and nickel in order to assess this scaling directly. We observe that the trapping of each of the alkanes studied decreases with the lattice stiffness and mass of the metal atom, but not as strongly as predicted by the lattice for constant itself. These observations are in general agreement with the expectations of molecular dynamic simulations, but further theoretical work is needed to understand the trends in detail.

Recent years have witnessed tremendous progress in the theoretical treatment of surfaces and processes on surfaces. A variety of surface properties can now be described from first principles, i.e. without invoking any empirical parameters. In this book the theoretical concepts and computational tools necessary and relevant for a microscopic approach to the theoretical description of surface science is presented. Based on the fundamental theoretical entity, the Hamiltonian, a hierarchy of theoretical methods is introduced. Furthermore, a detailed discussion of surface phenomena is given and comparisons made to experimental results made, making the book suitable for both graduate students and for experimentalists seeking an overview of the theoretical concepts in surface science.

The energetics and structures of clean and adsorbate covered surfaces are investigated in this dissertation. First, the formalism, within the Corrected Effective Medium (CEM) method, for calculating the surface energy of a clean surface is derived. The surface energies for many different metals and their low index surfaces are presented. The minimization of the surface energy is then used to predict the multilayer relaxation of the Al(111), (100), Ni(100), (110) and Fe(100) surfaces. Extensions of the surface CEM formalism to calculate the binding energies of ordered adsorbates on metals surfaces are also derived. The minimization of the binding energy allowed determination of the binding heights, sites and the extent of induced multilayer relaxation for H and N atoms on the Fe(110), (100) and W(110) surfaces. The last topic deals with the dynamics of the epitaxial growth of metals on metal surfaces. The CEM method was first modified by making approximations to enable faster evaluations of the potential and its corresponding forces for molecular dynamics simulations. The goal of these simulations was to identify the important steps in the formation of equilibrium epitaxial structures. 180 refs., 31 figs., 18 tabs.

This book gives a representative survey of the state of the art of research on gas-surface interactions. It provides an overview of the current understanding of gas surface dynamics and, in particular, of the reactive and non-reactive processes of atoms and small molecules at surfaces. Leading scientists in the field, both from the theoretical and the experimental sides, write in this book about their most recent advances. Surface science grew as an interdisciplinary research area over the last decades, mostly because of new experimental technologies (ultra-high vacuum, for instance), as well as because of a novel paradigm, the ‘surface science’ approach. The book describes the second transformation which is now taking place pushed by the availability of powerful quantum-mechanical theoretical methods implemented numerically. In the book, experiment and theory progress hand in hand with an unprecedented degree of accuracy and control. The book presents how modern surface science targets the atomic-level understanding of physical and chemical processes at surfaces, with particular emphasis on dynamical aspects. This book is a reference in the field.

"Molecular Sieves - Science and Technology" covers, in a comprehensive manner, the science and technology of zeolites and all related microporous and mesoporous materials. The contributions are grouped together topically in such a way that each volume deals with a specific sub-field. Volume 7 treats fundamentals and analyses of adsorption and diffusion in zeolites including single-file diffusion. Various methods of measuring adsorption and diffusion are described and discussed.