Photodissociation dynamics of CH2Br2 near 234 and 267 nm

The photodissociation dynamics of CH2Br2 was investigated near 234 and 267 nm. A two-dimensional photofragment ion velocity imaging technique coupled with a [2 + 1] resonance-enhanced multiphoton (REMPI) ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br (2P3/2) and Br* (2P1/2) atoms. The obtained translational energy distributions of Br and Br* are found consist of two components which should be come from the radical channel and secondary dissociation process, respectively. It is suggested that the symmetry reduction from C2vC2v to Cs during photodissociation invokes a non-adiabatic coupling between the 2B1 and A1 states. Consequently, the higher internal energy distribution of Br channel than Br* formation channel and the broader translational energy distribution of the former are presumed correlate with a variety of vibrational excitation disposal at the crossing point resulting from the larger non-adiabatic crossing from 2B1 to A1 state than the reverse crossing. Moreover, the measured anisotropy parameter β indicate that fragments recoil along the Br–Br direction mostly in the photodissociation.