Direct-Mode Chemical Reactions I: Methodology for Accurate Quantal Calculations

Abstract

Accurate quantum-mechanical state-to-state probabilities and cross sections for chemical reactions in three physical dimensions are just beginning to become available for selected neutral electronically adiabatic atom-diatom collision systems. Intense activity in a number of research groups, particularly since 1970, has led to the development of theoretical methods and computational algorithms which have been applied to several dozen model collinear reactions,(1–5) to several coplanar reactions,(6#x2013;10) and to the three-dimensional H + H2(11#x2013;14) and (to a lesser extent) F + H2(15) reactions. These results provide a body of knowledge against which approximate methods (particularly quantum approximations, Chapter 15, and classical mechanics, Chapter 18) may be compared. In addition, analysis of the quantum results, including state populations, probability density, and flux distributions in the transition state region, will surely provide us with a deeper understanding of “what happens during a chemical reaction.”