Dynamics of adsorption/desorption at solid surfaces

Abstract

Various theoretical approaches to the dynamics of sticking, thermal desorotion, and IR-photodesorption are reviewed. Depending on the approach, the aim of the theory is to calculate either state-to-state transition rates, or the probabilities of elementary events. Both formal developments, and the results of practical calculations are reviewed. Some relevant experimental results are also summarized. The quantum theory of sticking is presented from the time-dependent scattering, stationary scattering, and gettering theory points of view. At non-zero substrate temperatures, the existence of a sort of Wick's theorem simplifying the dynamics is important. The semi-classical approach (classical adsorbate, quantized substrate vibrations) is described in detail, and examples of its application to dissociative chemisorption, and rare-gas sticking are reviewed. Its application to IR-photodesorption is discussed briefly. Totally classical simulations of trapping, thermal desorption, and IR-photodesorption of rare-gas atoms are becoming routine, and the results of several such simulations are reviewed. Recent work on IR-photodesorption directs attention to Poincaré maps in analyzing the results. The modelling of dissociative chemisorption by quantum wavepacket evolution on a single potential energy surface is well-understood, but the inclusion of substrate vibrations and/or electronic excitations in the time evolution is a major task. For IR-photodesorption, the resonance-state decay model with, or without the participation of substrate phonons is reviewed. As well as being an important model in its own right, it also useful for obtaining insight into dealing classically, and quantum mechanically with “infrequent” events. Measurable desorption phenomena are often infrequent events. Practical results are obtained with a master-equation technique, and Golden Rule transition rates. The quantum theory of thermal desorption of rare-gas atoms from metals has been handled similarly, and angle-resolved time-of-flight spectra comprehensively computed.