From Ligand Field Theory to molecular collision dynamics: A common thread of angular momentum

Abstract

Interest in, and appreciation of, the role played by angular momentum in chemical physics was first aroused by a Carl Ballhausen lecture early in the author's scientific career. Later came deeper understanding of the fundamental nature of angular momentum and the power of its formal algebraic expression. Spectroscopy using light of precisely defined energy and (z-component of) angular momentum represents a unique experimental probe with the potential to reveal the underlying physics of chemical processes. Experiments using circularly polarised emission of gas phase molecules led to new insights in the field of molecular collision dynamics. Further work, and that of others, suggested an alternative formulation of the mechanics of bimolecular collisions. A theoretical model was developed guided throughout by experiment. Its basis is linear-to-angular momentum conversion within the constraint of state-to-state energy conservation. An evolutionary process guided by experiment is described, with illustrations that demonstrate the power of the angular momentum theory of molecular collisions developed by the author and co-workers. Examples include very recent work on multicollision models of gas ensembles of potential value in, e.g., modelling planetary atmospheres. © 2011 Springer-Verlag Berlin Heidelberg.