Photodissociation pathways in the simplest Criegee intermediate: a semi-classical investigation

Abstract

The dissociation of the simplest Criegee intermediate (H 2 COO) into formaldehyde (H 2 CO) and oxygen atom (O) is very important in the atmospheric chemistry. In this study, we investigate the photodissociation of the O–O bond of H 2 COO by simulating the dynamics of the process on the fitted multiconfigurational adiabatic potential energy surfaces (PESs). Tully’s fewest-switches surface hopping (FSSH) method is used for the simulation. The FSSH trajectories are initiated on the lowest optically-bright singlet excited state (S2) and propagated along the O–O coordinate. Some of the trajectories end up on energetically lower PESs as a result of radiationless transfer through conical intersections. However, all the trajectories lead to O–O bond dissociation via one of the two channels. The simulation results demonstrate that the restricted O–O motion dissociates H 2 COO into singlet fragments via the lower energy channel. The coupling of electronic states along O–O may account for this. Graphical abstract: The photodissociation of simplest Criegee intermediate (H2COO) into formaldehyde (H2CO) and oxygen (O) was studied using Tully's fewest-switches surface hopping (FSSH). The simulation results demonstrate that the restricted O–O motion dissociates into singlet fragments via the lower energy channel.[Figure not available: see fulltext.].