A two-dimensional wavepacket study of the nonadiabatic dynamics of CH2BrCl

The nonadiabatic photodissociation dynamics of CH2BrCl into CH2Br + Cl or CH2Cl + Br is studied using two-dimensional wavepacket propagations on ab initio multiconfigurational MS-CASPT2 potential energy surfaces. Using a three-state diabatic model, we investigate the electronic states responsible for the two competing fragmentation channels and how the conical intersection present between the two lowest excited states affects the dissociation rate. Within this model, we find that the Br/Cl branching ratio depends on the irradiation wavelength. Predominant C-Br fragmentation occurs for wavelengths longer than 200 nm, while nonadiabatic C-Cl dissociation with a constant branching ratio of 0.4 is predicted upon absorption of photons in the range of 170-180 nm. Additionally, we observe complete nonadiabatic population transfer in less than 100 fs, that is, before the wavepacket can reach the conical intersection. As a consequence, there is no three-body CH2 + Br + Cl dissociation.