Kinetic studies of atomic carbon, C[2p2(3PJ)], with small sulfur-containing molecules by time-resolved atomic resonance absorption spectroscopy in the vacuum ultra-violet

Abstract

We present a kinetic investigation of the reaction of atomic carbon in its electronic ground, C[2p2(3PJ)], with the small sulfur-containing molecules H2S, OCS, SO2 and CS2 by time-resolved atomic spectroscopy in the vacuum ultra-violet following the generation of C(23PJ) by the pulsed photolysis of C3O2. Decay profiles for atomic carbon were derived from resonance absorption at ? = 166 nm (33PJ?23PJ) using repetitive pulsing techniques coupled with signal averaging. Absolute rate data for the collisional removal of C(23PJ) by these gases were obtained as follows: kR (cm3 molecule?1 s?1, 300 K)?H2S 2.5 � 0.6 ? 10?10, OCS 5.6 � 0.2 ? 10?11, SO2 9.7 � 0.3 ? 10?11 and CS2 1.6 � 0.4 ? 10?10. Rate data for the reaction of atomic carbon with the photochemical precursor, necessary as an absolute kinetic standard, were obtained yielding k(C3O2) = 1.8 � 0.3 ? 10?10, in full agreement with previous investigations. The rate data in general were compared, where possible, with those derived from fast flow techniques and molecular beams for the particular case of H2S where overall insertion has been demonstrated with the detection of HCS and where H atom abstraction would be endothermic. The results in general are considered within the context of C atom reactions with sulfur-containing species in the interstellar medium.