Predissociation of state selected Br₂⁺ cations

High resolution ion imaging methods have been used to carry out a systematic investigation of the wavelength dependence of the recoil anisotropy of Br⁺(³P₂) fragments resulting from one photon dissociation of state selected Br₂⁺ cations in both spin-orbit components of their ²Π_g ground state and with both v″ = 0 and 1. The resonance structure so discerned is found to be concentrated in the energy gap between the ground [Br(²P_3/2) + Br⁺(³P₂)] and first excited [Br(²P_3/2) + Br⁺(³P₁)] dissociation limits, and to converge with increasing energy in a manner consistent with it being associated with a series of predissociating vibrational levels in a bound potential that correlates with the first excited dissociation asymptote. This resonance structure has been interpreted by performing spin-orbit averaged ab initio electronic structure calculations for all ungerade excited states of Br₂⁺ associated with the…σ_gπ_uπ_g*σ_u* valence space, incorporating spin-orbit effects semi-empirically, and then propagating wavepackets on the coupled diabatic potential energy curves so derived. These model calculations succeed in reproducing all of the trends observed experimentally, and provide much new insight into the non-adiabatic couplings amongst the various excited states of this textbook open-shell system.