Time-resolved Atomic Spectroscopy Research Articles

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

We present a kinetic investigation of the reaction of atomic carbon in its electronic ground, C[2p 2( 3P J)], with the small sulfur-containing molecules H 2S, OCS, SO 2 and CS 2 by time-resolved atomic spectroscopy in the vacuum ultra-violet following the generation of C(2 3P J) by the pulsed photolysis of C 3O 2. Decay profiles for atomic carbon were derived from resonance absorption at λ = 166 nm (3 3P J–2 3P J) using repetitive pulsing techniques coupled with signal averaging. Absolute rate data for the collisional removal of C(2 3P J) by these gases were obtained as follows: k R (cm 3 molecule −1 s −1, 300 K)—H 2S 2.5 ± 0.6 × 10 −10, OCS 5.6 ± 0.2 × 10 −11, SO 2 9.7 ± 0.3 × 10 −11 and CS 2 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(C 3O 2) = 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 H 2S 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.

Kinetic Studies of Atomic Carbon, C[2p2 (3PJ)], with Thiols by Time-Resolved Atomic Resonance Absorption Spectroscopy in the Vacuum Ultraviolet

Reaction rates of atomic carbon in its electronic ground state, C[2p2 (3PJ)], with a range of large sulfur-containing molecules have been investigated using time-resolved atomic spectroscopy in the vacuum ultraviolet following pulsed irradiation. Absolute rate data for the collisional removal at 300 K of C(23PJ) by the gases 1-propanethiol, 1-butanethiol, 1-pentanethiol, 2-propanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol and dimethyl sulfide are reported. All processes proceed at rates of the order of the collision numbers, supporting an overall mechanism of C-atom insertion into the S–H bond following initial addition, which is energetically favourable, a mechanism demonstrated analogously hitherto with H2S and where H-atom abstraction would also be endothermic.