SPIN-ORBIT BRANCHING IN THE PHOTODISSOCIATION OF HBR - TIME-INDEPENDENT, TIME-DEPENDENT, AND SEMICLASSICAL CALCULATIONS

The dynamics of the photofragmentation of HBr is treated within time-i ndependent, time-dependent, and semiclassical methods. The calculated relative cross sections for formation of the two accessible fine-struc ture channels [Br(P-2(1/2)) and Br(P-2(3/2))] agree well with the expe rimental results, both in magnitude and in dependence on photon excita tion wavelength. For relatively small photon wavelength (lambda = 193 nm), vertical excitation in the Franck-Condon region populates prefere ntially the A (1) Pi state, and only three states (A (1) Pi, the Omega = 1 components of the a (3) Pi and 1 (3) Sigma(+)), coupled by the sp in-orbit interaction, are invoved in the dissociation process. For lar ger photon wavelength (lambda = 243 nm), the product branching is gove rned by initial excitation in both the A (1) Pi state and the a (3) Pi (Omega = 0) component. Comparison of the redistribution of the time-in dependent photofragment fluxes as a function of the H-Br separation wi th the temporal evolution of the populations within a time-dependent f ramework shows that the two methods, although based on a different poi nt of view, provide equivalent mechanistic information on the dissocia tion process. (C) 1997 American Institute of Physics.