Direct Dynamics Simulations of Unimolecular Dissociation of 1,2-dioxetane

Abstract

A detailed study of the dynamics of unimolecular dissociation of 1,2-dioxetane (DO) using direct chemical dynamics simulations is presented. Of special interest is the comparison of the dissociation kinetics with the predictions of RRKM theory and implication to the intramolecular vibrational energy redistribution in the molecule. In the process, instabilities observed in unrestricted direct dynamics simulations of homolytic bond dissociation and diradical formation are tackled. A simple and convenient algorithm has been used to circumvent the energy conservation issues related to these instabilities and obtain reliable trajectory simulations. Dissociation probabilities obtained for various initial vibrational excitations are presented and compared with each other and with classical harmonic RRKM theory. DO is found to exhibit intrinsic non-RRKM behavior which is attributed to a) the presence of quasiperiodic trajectories trapped in the phase space ; b) bottlenecks in the IVR between vibrational modes inside and outside the ring.