An ab initio study of the photodissociation of CH 2 I and CH 2 I .

Photodissociation of the CH 2 I radical and the CH 2 I + cation is studied by means of high-level ab initio calculations, including spin-orbit effects. Potential-energy curves (PEC) along the dissociating bond distances involved in some fragmentation pathways of these species are computed for the ground and several excited electronic states. Based on the PECs obtained, the possible photodissociation mechanisms are analyzed and suggested. Significant differences are found between the fragmentation dynamics of the neutral radical and that of the cation. While a relatively simple dissociation dynamics is predicted for CH 2 I, more complex fragmentation mechanisms involving internal conversion and couplings between different excited electronic states are expected for CH 2 I + . The species studied here are relevant to atmospheric chemistry, and the present work can help to understand better how their photodissociation may affect chemical processes in the atmosphere.