Unimolecular dissociation dynamics of vibrationally activated CH3CHOO Criegee intermediates to OH radical products.

Abstract

The hydroxyl radical is an important atmospheric oxidant, and a significant source of its production occurs through alkene ozonolysis. This takes place via a cycloaddition reaction and subsequent fragmentation to form an energized carbonyl oxide (for example, CH3CHOO), known as a Criegee intermediate, which can then either react with another atmospheric species or decay and, in doing so, produce the hydroxyl radical. Here, we examine the dissociation dynamics of a prototypical Criegee intermediate by characterizing the translational and internal energy distributions of the OH radical products, which reflect critical configurations along the reaction pathway. Experimentally, the kinetic energy release to OH products is ascertained through velocity map imaging. Theoretically, quasi-classical trajectories are performed on a new full-dimensional, ab initio potential energy surface. Both experiment and theory show that most of the available energy flows into internal excitation of the vinoxy products. The isotropic angular distribution of OH fragments indicates that dissociation occurs in ≥2 ps, in agreement with theory.