Table of Contents
Laser Chemistry
Volume 2, Issue 5-6, Pages 243-252

On the Question of Mode-Specificity in Unimolecular Reaction Dynamics

Department of Chemistry, Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720, California, USA

Copyright © 1983 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Unimolecular decomposition following state-specific laser excitation is considered. If the transition state for the unimolecular reaction possesses any geometrical symmetry, then it is shown that this can lead to mode-specificity in the decay rates (i.e., different states with essentially the same total energy and angular momentum react at significantly different rates). This is illustrated for a model problem of two coupled oscillators (the Henon–Heiles potential) and also for the unimolecular dissociation of formaldehyde, H2CO→H2+CO, which has a planar transition state. Dynamical calculations indicate that there may also be a significant degree of mode-specificity for the formaldehyde reaction beyond that due to symmetry.