Imaging the [1+1] two-photon dissociation dynamics of Br2+ in a cold ion beam

Abstract

The [1+1] two-photon dissociation dynamics of mass-selected 79Br2+ has been studied in a cold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer. The quartet 14Σu,3/2− state of 79Br2+ is employed as an intermediate state to initiate resonance enhanced two-photon excitation to high-lying dissociative states in the 4.0–5.0 eV energy region above the ground rovibronic state. Total kinetic energy release (TKER) and the two-dimensional recoiling velocity distributions of fragmented 79Br+ ions are measured using the technique of DC-slice velocity map imaging. Branching ratios for individual state-resolved product channels are determined from the TKER spectra. The measured photofragment angular distributions indicate that the dissociation of 79Br2+ occurs in dissociative Ω=3/2 state via ΔΩ=0 parallel transition from the 14Σu,3/2− intermediate state. Due to the considerable spin-orbit coupling effects in the excited states of 79Br2+, higher-lying dissociative quartet states are likely responsible for the observed photodissociation processes.