Velocity map imaging study of BrCl photodissociation at 467 nm: Determination of all odd-rank (K=1 and 3) anisotropy parameters for the Cl(P3∕22) photofragments

Resonance-enhanced multiphoton ionization and velocity map imaging of the Cl(P3∕202) fragments of BrCl photolysis at 467.16 nm have been used to obtain a complete set of orientation parameters (with ranks K=1 and 3) describing the polarization of the electronic angular momentum. The experiments employ two geometries distinguished only by the circular or linear polarization of the photolysis laser beam. Normalized difference images constructed from the data accumulated using a right or left circularly polarized probe-laser beam, counterpropagating with the photolysis laser, were fitted to basis images corresponding to contributions from various odd-rank anisotropy parameters. Expressions are given for the difference images in terms of the K=1 and 3 anisotropy parameters, which describe coherent and incoherent parallel and perpendicular excitation and dissociation mechanisms. The nonzero values of the anisotropy parameters are indicative of nonadiabatic dissociation dynamics, with likely contributions from flux on the AΠ3(1),BΠ3(0+),CΠ1(1), and XΣ+1(0+) states as well as one further Ω=1 state, all of which correlate adiabatically to Cl(P3∕202)+Br(P3∕202) photofragments. The magnitudes of the parameters depend both on the amplitudes of dissociative flux in these states, and also on the phases accumulated by the nuclear wave functions for different dissociation pathways.