Trajectory study of collision complex formation. Weak to strong coupling transition in atom-diatomic molecule collisions

Abstract

Accurate and detailed classical trajectory calculations based on a 15th-order Gauss-Radau method are used to study the transition from weak to strong coupling in the formation of triatomic collision complexes. The model systems studied represent K + NaCl and O ( 1D) + H 2. The aim is to determine the applicability of simple statistical theories in which either weak or strong coupling is assumed. Global as well as local criteria for weak or strong coupling are proposed and found to give similar results indicating a rapid transition from weak to strong coupling in a narrow transition zone of separations. The complex formation cross sections are compared with corresponding predictions of four different statistical theories including the microcanonical variational transition state theory and a related effective potential theory based on a weak coupling assumption.