Determination of the rate constant and product channels for the radical-radical reaction NCO(X 2Π) + C2H5 (X 2 A") at 293 K

The rate constant and product branching ratios for the reaction of the cyanato radical, NCO (X (2)Pi), with the ethyl radical, C2H5 (X (2)A"), have been measured over the pressure range of 0.28 to 0.59 kPa and at a temperature of 293 +/- 2 K. The total rate constant, k(1), increased with pressure, P(kPa), described by k(1) = (1.25 +/- 0.16) x 10(-10) + (4.22 +/- 0.35) x 10(-10) p cm(3) molecule(-1) S-1. Three product channels were observed that were not pressure dependent: (1a) HNCO + C2H4 k(1a) = (1.1 +/- 0.16) x 10(-10), (1b) HONC + C2H4, k(1b) = (2.9 +/- 1.3) x 10(-11), (1c) HCN + C2H4O, k(1c) = (8.7 +/- 1.5) x 10(-13), with units cm(3) molecule(-1) s(-1) and uncertainties of one-standard deviation in the scatter of the data. The pressure dependence was attributed to a forth channel, (1d), forming recombination products C2H5NCO and/or C2H5OCN, with pressure dependence: (1d) k(1d) = (0.090 +/- 1.3) x 10(-11) + (3.91 +/- 0.27) x 10(-10) p cm(3) molecule(-1) s(-1). The radicals were generated by the 248 nm photolysis of CINCO in an excess Of C2H6. Quantitative infrared time-resolved absorption spectrophotometry was used to follow the temporal dependence of the reactants and the appearance of the products. Five species were monitored, HCl, NCO, HCN, HNCO, and C2H4, providing a detailed picture of the chemistry occurring in the system. Other rate constants were also measured: CINCO + C2H5, k(10) = (2.3 +/- 1.2) x 10(-13), NCO + C2H6, k(2) = (1.6 +/- 0.11) x 10(-14), NCO + C4H10, k(4) = (5.3 +/- 0.51) x 10(-13), with units cm(3) molecule(-1) s(-1) and uncertainties of one-standard deviation in the scatter of the data.