Introduction

Abstract

The physical chemist is accustomed to studying various rate processes in chemical systems, particularly chemical reactions, on the macroscopic level. To understand the molecular behavior of the systems observed macroscopically, the physical chemist is then compelled to resort to various statistical mechanical methods which tend to average out some interesting and useful information that otherwise might have been observed. This limitation has begun to be lifted since the mid fifties owing to the pioneering work of Taylor and Datz [1.1] on the application of the molecular-beam technique to chemical reactions, which enabled them to study molecular events. The potential of their work was quickly appreciated by many researchers [1.2] and the field has now grown to a full-fledged discipline which influences thinking in other branches of physical chemistry, such as spectroscopy [1.3] and photochemistry [1.4]. Like other experimental disciplines, molecular-beam studies have created numerous theoretical questions that challenge theoreticians and experimentalists alike, the enormous volume of literature on atomic and molecular scattering theories attesting to the activity in the field.