LOW-TEMPERATURE RATE COEFFICIENTS FOR REACTIONS OF ETHYNYL RADICAL (C2H) WITH PROPANE, ISOBUTANE, N-BUTANE, AND NEOPENTANE

Low-temperature rate coefficients for the reactions of C2H + RH --> pr oducts (RH = C3H8, i-C4H10, n-C4H10, and neo-C5H12) have been measured over the temperature range 154-361. K. Measurements were made using l aser photolysis of C2H2 to produce C2H. Transient infrared laser absor ption decays of C2H are used to monitor the subsequent reaction in a t ransverse flow eel. The results show that the rate coefficients for th e reactions of C2H with propane are independent of temperature while t he rate coefficients for the reactions of C2H with isobutane, n-butane , and neopentane have a negative temperature dependence. Over the expe rimental temperature range, the rate constants for C2H + RH fit the fo llowing Arrhenius expressions: k(propane) = (7.8 +/- 0.4) x 10(-11) ex p[(3 +/- 12)/T], k(isobutane) = (8.7 +/- 0.8) x 10(-11) exp[(28 +/- 21 )/T], k(n-butane) = s(-1). The corresponding rate constants at 298 K a re k(propane) = 7.9 x 10(-11), k(isobutane) = 9.6 x 10(-11), k(n-butan e) = 1.2 x 10(-10), k(neopentane) = 1.1 X 10(-10) cm(3) molecules(-1) s(-1).