KINETIC INVESTIGATION OF THE REACTIONS OF GROUND-STATE ATOMIC CARBON, C(2P2(3PJ)), WITH ACETYLENES BY TIME-RESOLVED ATOMIC RESONANCE - ABSORPTION-SPECTROSCOPY IN THE VACUUM ULTRA-VIOLET

Kinetic investigations are described of the reactions of ground state atomic carbon, (C(2p2(PJ)))-P-3, monitored by time-resolved atomic resonance absorption spectroscopy, for a range of acetylenic collision partners and with 1,3-Butadiene. Atomic carbon was generated by the repetitive pulsed irradiation (lambda > ca. 160 nm) of C3O2 in the presence of excess helium buffer gas and the added reactant gases in a slow flow system, kinetically equivalent to a static system. (C(2PJ))-P-3, was then monitored photoelectrically by time-resolved atomic resonance absorption in vacuum ultra-violet (lambda = 166 nm, 3P-3J <-- 2P-3J) with direct computer interfacing for data capture and analysis. The following absolute second-order rate constants for the reactions of (C(2PJ))-P-3 with the following acetylenes are presented using the previously reported rate data for (C(2PJ))-P-3 + C3O2: [GRAPHICS] The rate constant for reaction with 1,3-Butadiene was also measured and found to be (k(R)(C(2PJ))-P-3 + 1,3-Butadiene (300K)) = 11.2 +/- 0.6 x 10(-10) cm3 molecule-1 s-1. These results, compared with the analogous body of absolute rate data for atomic silicon in its (Si(3p2(PJ)))-P-3 ground state, also determined hitherto by time-resolved atomic resonance absorption spectroscopy, demonstrate similar kinetic behaviour, and constitute the first reported body of absolute rate data for these reactions of ground state carbon with acetylenes. The result for acetylene, itself, is greater by at least six orders of magnitude than the previous estimate, derived from indirect measurements in a flow system. The results for 2-Butyne and 1,3-Butadiene are compared both with absolute rate data for (Si(3PJ))-P-3, and also with the results of nuclear recoil measurements of Si-31 and (CH3)2Si derived from pyrolytic investigations on collision with these molecules.