Slice imaging of quantum state-to-state photodissociation dynamics of OCS

Abstract

Slice imaging experiments are reported for the quantum state-to-state photodissociation dynamics of OCS. Both one-laser and two-laser experiments are presented detecting CO(J) or S(¹D₂) photofragments from the dissociation of hexapole state-selected OCS(v₂ = 0,1,2 | J = 1,2) molecules. We present data using our recently developed large frame CCD centroiding detector and have implemented a new high speed MCP high voltage pulser with an effective slice width of only 6 ns. Slice images are presented for quantum state-to-state photolysis, near 230 nm, of vibrationally excited OCS(v₂ = 0,1,2). Two-laser pump–probe experiments detecting CO(J = 63 or 64) show a dramatic change in the β parameter for the same final state of CO(J) when the photolysis energy is reduced by about 1000 cm⁻¹. We attribute the observed change from large positive to large negative β to a large increase of the molecular frame deflection angle at very slow recoil velocity, due to a breakdown of the axial recoil. Two-laser experiments on the S(¹D₂) fragment reveal single well-separated rings in the slice images correlating with individual CO(J) states. Strong polarization effects of the probe laser are observed, both in the angular distribution of the intensity of single S(¹D₂) rings and in the resolution of the radial velocity distribution. It is shown how the broadening of the velocity distribution can be reduced by a directed ejection of the electron in the ionization process perpendicular to the slice imaging plane. The dissociation energy of OCS(v₂ = 0, J = 0) → CO(J = 0) + S(¹D₂) is determined with high accuracy D₀ = (34 608 ± 24) cm⁻¹.