Quantum interference and asymptotic interactions in the photodissociation of SH: Total cross section and branching ratios

Abstract

A theoretical analysis is presented for the photodissociation processes of SH to S(P-3) and S(D-1). Transition dipole moments from the ground X (2)Pi state to the A (2)Sigma (+), (2)Sigma (-), (2)Delta, 2 (2)Pi states are computed by the effective valence shell Hamiltonian method. Two frame transformation matrices are constructed and used to describe the correlations between the two sulfur atomic terms [S(P-3) and S(D-1)] and the adiabatic Born-Oppenheimer molecular states. Very interesting dynamics of quantum interference effects and asymptotic interactions are found. At energies between the thresholds to the S(P-3) and S(D-1) limits, the resonances are mostly Lorentzian with more or less constant S(P-3(j),j=0,1,2) branching ratios. The effects of the intrastate interactions between the repulsive states are predicted to be very strong. At energies above the threshold to S(D-1) limit, quantum interferences between the dissociative pathways through the optically bright repulsive states (A (2)Sigma (+), (2)Sigma (-), (2)Delta, and 2 (2)Pi states) are predicted to give asymmetric resonances of multichannel character. Partial cross sections to the triplet sulfur fine structure states S(P-3(j),j=0,1,2) exhibit different degrees of asymmetry and, consequently, the S(P-3(j),j=0,1,2) branching ratios display strong variations across the asymmetric resonances, suggesting the possibility of controlling the product distributions by scanning the excitation wavelengths across a single asymmetric resonance in a one-photon excitation process. At higher energies, the interference between the two direct dissociation routes (by A (2)Sigma (+) and (2)Sigma (-) states) is shown to produce highly oscillatory variations of the total cross section for dissociation to S(P-3) and of the branching ratios of S(P-3(j),j=0,1,2). (C) 2001 American Institute of Physics.