Product state distributions of vibrationally excited CO(v) for the CH(X2II) and CH(A2Δ) channels of the C2H+O(3P) reaction

The C2H + O(P-3) reaction is investigated using time-resolved Fourier transform infrared spectroscopy (TR-FTIR). The CH and O radicals are produced by 193-nm photolysis of C2H2 and SO2 precursors. Multiple vibrationally excited products are observed from several resulting reaction processes, including products: CO, CO2, C4H2, and CH. For this choice of photolytic precursors, it is observed that the C2H + SO2, C2H2 + O, and the HCCO + O reactions contribute to the observed product signals. To evaluate the contribution of the C2H + SO2 reaction to the removal kinetics of C2H in the C2H2/SO2 system, the room-temperature rate constant for the C2H + SO2 reaction is experimentally determined to be k = (1.1 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1). The time dependencies of the CO and CO2 species are measured experimentally and simulated to determine conditions under which contributions from the several processes that give the same product can be differentiated. Analysis of the nascent vibrational distribution of the CO products from C2H + O suggests the participation of both CH(A(2)Delta) and CH(X(2)Pi) products, in the ratio of similar to3:2. The surprisal parameters for the vibrational distribution of the CO products of these two channels are found to be -1.5 +/- 0.2 and -1.1 +/- 0.2, respectively. It is suggested that the reaction proceeds through the HCCOdouble dagger intermediate, in agreement with earlier studies, but the CH(A(2)Delta)/CH(X(2)Pi) branching fraction may be larger than previously reported.