Absolute rate data for the reactions of ground-state atomic carbon, C[2p2(3PJ)], with alkenes investigated by time-resolved atomic resonance absorption spectroscopy in the vacuum ultraviolet

Abstract

The collisional behaviour of ground-state atomic carbon, C[2p²(³P_J)], monitored by time-resolved atomic resonance absorption spectroscopy, is reported for reactions with a wide range of alkenes. Atomic carbon was generated and studied in a modified vacuum ultraviolet experimental system similar to that employed hitherto by the repetitive pulsed irradiation (λ≳ 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(2 ³P_J) was then monitored photoelectrically by time-resolved atomic resonance absorption in vacuum UV (λ= 166 nm, 3 ³P_Jâ†� 2 ³P_J) with direct computer interfacing for data capture and analysis. The following absolute second-order rate constants for the reactions of C(2 ³P_J) with the following alkenes are reported: [graphic omitted] These results, constituting the first reported body of absolute rate data for reactions of ground-state carbon with alkenes, are compared with the analogous body of absolute rate data for atomic silicon in its Si[3p²(³P_J)] ground state, also determined hitherto by time-resolved atomic resonance absorption spectroscopy and demonstrating similar kinetic behaviour. The result for ethene is greater by at least six orders of magnitude than the previous estimate derived from indirect measurements on a flow system and is in accord with earlier considerations of the nature of the potential surface for collision. The result for reaction of C(2 ³P_J) with C₃O₂[k_R/cm³ molecule^–1 s^–1(300 K)=(1.8 ± 0.1)× 10^–10] is found to be in accord with earlier measurements.