An experimental and ab initio reinvestigation of the Lyman-alpha photodissociation of H2S and D2S

The Lyman-alpha (lambda (H) = 121.6 nm) photodissociation of both H2S and D 2S has been reinvestigated using the experimental technique of H/D atom pho tofragment translational spectroscopy. Their total kinetic energy release p rofiles consist of two distinct components. The first, which is highly stru ctured, is assigned to two body dissociation to H/D(S-2) + SH/SD(A (2)Sigma (+)) fragments, with the latter formed in a range of rovibrational states. By assigning these various levels the dissociation energy of D2S (measured relative to the lowest rovibrational level of the products) is determined to be D-0(D-SD) greater than or equal to 31 874+/-22 cm(-1). The second con tribution, which is broad and relatively unstructured, is modeled in terms of two likely fragmentation pathways; secondary predissociation of SH/SD(A (2)Sigma (+)) partner fragments associated with the structured contour, and primary three-body dissociation to 2H/D(S-2) + S(D-1) atomic products. The presented data allow determination of the kinetic energy-dependent anisotr opy parameter (beta), which is positive over both profiles. This indicates a preferentially parallel distribution of H/D atom recoil velocities about the laser polarization axis. These data are presented in tandem with ab ini tio and classical trajectory calculations which seek to explain the lack of branching to ground state H/D+SH/SD(X (2)Pi (Omega)) molecular products. T he analogous channel is important in the Lyman-alpha dissociation of the li ghter homologue, H2O. (C) 2001 American Institute of Physics.