Photodissociation Dynamics of CH2OO on Multiple Potential Energy Surfaces: Experiment and Theory.

Abstract

UV excitation of the CH2OO Criegee intermediate across most of the broad span of the (B1A')-(X1A') spectrum results in prompt dissociation to two energetically accessible asymptotes: O (1D) + H2CO (X1A1) and O (3P) + H2CO (a3A''). Dissociation proceeds on multiple singlet potential energy surfaces that are coupled by two regions of conical intersection (CoIn). Velocity map imaging (VMI) studies reveal a bimodal total kinetic energy release (TKER) distribution for the O (1D) + H2CO (X1A1) products with the major and minor components accounting for ca. 40% and ca. 20% on average of the available energy (Eavl), respectively. The unexpected low TKER component corresponds to highly internally excited H2CO (X1A1) products accommodating ca. 80% of Eavl. Full dimensional trajectory calculations suggest that the bimodal TKER distribution of the O (1D) + H2CO (X1A1) products originates from two different dynamical pathways: a primary pathway (69%) evolving through one CoIn region to products and a smaller component (20%) sampling both CoIn regions enroute to products. Those that access both CoIn regions likely give rise to the more highly internally excited H2CO (X1A1) products. The remaining trajectories (11%) dissociate to O (3P) + H2CO (a3A'') products after traversing through both CoIn regions. The complementary experimental and theoretical investigation provides insight on the photodissociation of CH2OO via multiple dissociation pathways through two regions of CoIn that control the branching and energy distributions of products.