Reactions of hot deuterium atoms with OCS in the gas phase and in OCS–DI complexes

Abstract

Reactions of photolytically prepared hot deuterium atoms with OCS have been investigated: (i) under gas phase, single collision, arrested relaxation (i.e., bulk) conditions; and (ii) by photoinitiating reactions within weakly bound OCS–DI complexes. Nascent SD(X 2Π, v=0) rotational, spin–orbit, and Λ-doublet populations were obtained for the photolysis wavelengths 250, 225, and 223 nm by using A 2Σ←X 2Π laser induced fluorescence (LIF). The reason for using deuterium is strictly experimental: A 2Σ predissociation rates are considerably smaller for SD than for SH. The SD (v=0) rotational distribution was found to be very cold and essentially the same for both bulk and complexed conditions; the most probable rotational energy is ∼180 cm−1. No bias in Λ-doublet populations was detected. Spin–orbit excitation for bulk conditions was estimated to be [2Π1/2]/[2Π3/2]∼0.25, where 2Π1/2 is the upper spin–orbit component. This ratio could not be obtained with complexes because of limited S/N. The complete set of present and past experimental findings, combined with recent theoretical results of Rice, Cartland, and Chabalowski suggest a mechanism in which SD derives from a very short lived HSCO precursor. This can result from direct hydrogen attack at the sulfur and/or the transfer of hydrogen from carbon to sulfur via the HCOS intermediate.