Photodissociation Dynamics of <em>o</em>-Bromotoluene at 234 and 267 nm

Abstract

The photodissociation of o-bromotoluene was studied at 234 and 267 nm using velocity map imaging combined with a resonance-enhanced multiphoton ionization (REMPI) technique. Translational energy distributions suggested that ground state Br (2P(subscript 3/2)) and spin-orbit excited state Br(superscript *) (2P(subscript 1/2)) fragments were all generated via two dissociation channels: a fast channel and a slow channel. The anisotropy parameters of the fast channels were determined to be 1.15 (Br) and 0.55 (Br(superscript *)) at 234 nm, 0.90 (Br) and 0.60 (Br(superscript *)) at 267 nm. The anisotropy parameters of the slow channels were 0.12 (Br) and 0.14 (Br(superscript *)) at 234 nm, 0.11 (Br) and 0.10 (Br(superscript *)) at 267 nm. The Br and Br(superscript *) fragments of the slow channel were less anisotropic than those of the fast channel. The total relative quantum yields of Br (Φ (Br)) were 0.67 at 234 nm and 0.70 at 267 nm. Ground state Br (2P(subscript 3/2)) was the main product from the photolysis of o-bromotoluene at 234 and 267 nm. We propose that the fast channel originates from excitation of bound excited singlet (π, π(superscript *)) states followed by predissociation along repulsive (n, σ(superscript *)) states. The anisotropy parameters of the slow channels were close to zero indicating a hot dissociation mechanism on a highly vibrational ground state followed the internal conversion of the excited singlet state.