The dynamics of Br( ²P _j) formation in the photodissociation of vinyl and perfluorovinyl bromides

The photodissociation dynamics of vinyl bromide and perfluorovinyl bromide have been investigated at 234 nm using a photofragment ion imaging technique coupled with a state-selective [2+1] resonance-enhanced multiphoton ionization scheme. The nascent Br atoms stem from the primary C-Br bond dissociation leading to the formation of C ₂H ₃(X̃) and Br( ²P _j;j=1/2,3/2). The obtained translational energy distributions have been well fitted by a single Boltzmann and three Gaussian functions. Boltzmann component has not been observed in the perfluorovinyl bromide. The repulsive ³A ^′(n, σ ^*) state has been considered as the origin of the highest Gaussian components. Middle translational energy components with Gaussian shapes are produced from the ¹A ^″(π, σ ^*) and/or ³A ^″(π, σ ^*) which are very close in energy. Low-energy Gaussian components are produced via predissociation from the ³A ^′(π,π ^*) state. The assignments have also been supported by the recoil anisotropy corresponding to the individual components. It is suggested that intersystem crossing from the triplet states to the ground state has been attributed to the Boltzmann component and the fluorination reduces the probability of this electronic relaxation process.