Photodissociation of carbonic dibromide at 267 nm: Observation of three-body dissociation and molecular elimination of Br2

Abstract

The photodissociation of Br2CO around 267 nm has been studied by time-of-flight mass spectroscopy and ion velocity imaging. The atomic (Br and Br*) and molecular products (Br2 and BrCO) are detected via multiphoton ionization with the same laser. The results show that the molecule dissociates into (1) Br(fast)+Br(slow)+CO via an asynchronously concerted three-body decay process for both ground and spin–orbit excited bromine atoms, (2) BrCO(A)+Br, and (3) Br2+CO, the molecular elimination channel. The translational energy distributions of bromine atoms from reaction (1) are bimodal. For both spin–orbit states the anisotropy parameters differ clearly for slow and fast bromine atoms, where the β values for slow bromine atoms decrease relative to those for fast atoms. The β values for the Br2 elimination channel almost reach the low limit of −1. Taking into account the translational energy and angular distributions of these reactions, an asynchronously concerted decay mechanism could be proposed for the three-body dissociation. It is concluded that the transition dipole moment is in the direction perpendicular to the C=O bond in the initial excitation, which is also consistent with all the observations for reactions (2) and (3).