REDUCED DIMENSIONALITY THEORY OF QUANTUM REACTIVE SCATTERING

We review reduced dimensionality theories of quantum reactive scattering for systems with activation barriers in which a subset of the full number of degrees of freedom are coupled together. The emphasis in this article is on a particular theory in which the internal bending/angular motion of a reaction system is treated adiabatically. Additional approximations in the spirit of transition-state theory are reviewed and shown to be quite accurate and useful. Example systems include the O(P3) + H-2 reaction and the paradigm H + H-2 reaction, for which new comparisons are made with recent accurate three-dimensional calculations. Not only do these atom-diatom examples illustrate the quantitative accuracy of the reduced dimensionality/adiabatic bend theory, but also they clearly demonstrate the existence of quantized transition states. These are quantum states of the three-atom transition states that are responsible for the steplike energy dependence of the cumulative reaction probability. A brief review of recent applications of the reduced dimensionality theory to photodetachment spectroscopy of the transition state is also given. Finally, we review the recent extension of the reduced dimensionality theory to diatom-diatom reactions and illustrate the method to the H-2 + CN reaction.