Photodissociation of HBr: 1. Electronic structure, photodissociation dynamics and vector correlation coefficients

Abstract

Ab initio potential energy curves, transition dipole moments and spin-orbit coupling matrix elements are computed for HBr. These are then used, within the framework of time-dependent quantum mechanical wavepacket calculations to study the photodissociation dynamics of the molecule. Total and partial integral cross sections, the branching fraction for the formation of excited state bromine atoms Br(²P_1/2), and the lowest order anisotropy parameters $\beta$ for both ground and excited state bromine are calculated as a function of photolysis energy and compared with previously determined experimental and theoretical data. Higher order anisotropy parameters are computed for the first time for HBr and compared with recent experimental measurements. A new expression for the Re[a⁽³⁾₁(||,\perp)] parameter describing coherent parallel and perpendicular production of ground state bromine in terms of the dynamical functions is given. While good agreement is obtained between the theoretical predictions and the experimental measurements, the discrepancies are analysed to establish how improvements might be achieved. Insight is obtained into the non-adiabatic dynamics by comparing the results of diabatic and fully adiabatic calculations.

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