Imaging the Dynamics of CH2BrI Photodissociation in the Near Ultraviolet Region

The photodissociation dynamics of jet-cooled CH2BrI were investigated in the near-ultraviolet (UV) region from 280-310 nm using velocity map imaging. We report the translational and internal energy distributions of the CH2Br radical and ground state I (2 P3/2) or spin-orbit excited I (2 P1/2) fragments determined by velocity map imaging of the ionized iodine fragments following 2 + 1 resonance-enhanced multiphoton ionization of the nascent neutral iodine products. The velocity distributions indicate that most of the available energy is partitioned into the internal energy of the CH2Br radical with only modest translational excitation imparted to the cofragments, which is consistent with a simple impulsive model. Furthermore, from extrapolation of the velocity distribution results, the first determination of the C-I bond dissociation energy of CH2BrI is presented in this work to be D0 = 16 790 ± 590 cm-1. The ion images appear anisotropic, indicative of a prompt dissociation, and the derived anisotropy parameters are consistently positive. Additionally, the angular distributions report on the electronic excited state dynamics, which validate recent works characterizing the electronic states responsible for the first absorption band of CH2BrI. In the current work, photolysis of CH2BrI on the red edge of the absorption spectrum reveals an additional channel producing I (2 P3/2) fragments.