Direct Observation of the Primary and Secondary C-Br Bond Cleavages from the 1,2-Dibromopropane Photodissociation at 234 and 265 nm Using the Velocity Map Ion Imaging Technique

Photodissociation dynamics of 1,2-dibromopropane has been investigated at 234 and 265 nm by using the velocity map ion imaging method. At both pump energies, a single Gaussian-shaped speed distribution is observed for the Br*(2P1/2) fragment, whereas at least three velocity components are found to be existent for the Br(2P3/2) product. The secondary C−Br bond cleavage of the bromopropyl radical which is energized from the ultrafast primary C−Br bond rupture should be responsible for the multicomponent translational energy distribution at the low kinetic energy region of Br(2P3/2). The recoil anisotropy parameter (β) of the fragment from the primary C−Br bond dissociation is measured to be 0.53 (0.49) and 1.26 (1.73) for Br(2P3/2) and Br*(2P1/2), respectively, at 234 (265) nm. The β value of Br(2P3/2) from the secondary C−Br bond dissociation event at 265 nm is found to be 0.87, reflecting the fact that the corresponding Br(2P3/2) fragment carried the initial vector component of the bromopropyl radical pro...