Dynamics of Br(2Pj) Formation in the Photodissociation of Bromobenzene

Summary In the present study, the photodissociation dynamics of bromobenzene (C 6 H 5 Br) has been investigated at 234 nm using a photofragment ion-imaging tec hnique coupled with a state- selective REMPI scheme. In C 6 H 5 Br, the nascent Br atoms are produced from the primary C-Br bond dissociation, which leads to the formation of C 6 H 5 ( X %) and Br ( 2 P j , j = 1/2, 3/2). The obtained translational energy distributions were well fitted by a single Boltzmann function and two Gaussian functions. On the basis of the potential energy surfaces obtained from recent multireference CASSCF and CASPT2 calculations, the lowest- energy Gaussian components we re assigned to the curve cro-ssing from the initially pumped B 2 1 (π,π*) state to the repulsive B 1 3 ( n ,σ*) state. The highest accessible B 1 3 ( n ,σ*) state has been considered to be the origin of the highest Gaussian components. The observed recoil anisotropy and width of the Gaussian func-tions were also consistent with the abovementioned assign-ment. Finally, it is suggested that the intersystem crossing follow-ed by the excitation from the singlet