Rate of the reaction of hydroxyl radical with acetylene

The kinetics of the decay of hydroxyl radicals in the presence of excess acetylene were studied at pressures in the vicinity of 1 torr and at ambient temperature in a tubular discharge-flow reactor. Hydroxyl radicals were produced by the reaction of atomic hydrogen with nitrogen dioxide, H + NO2 OH + NO. The concentration of hydroxyl was followed by line absorption photometry at 308.939 nm and 308.328 nm. Second-order rate coeffcients were determined in two sets of experiments. The initial concentration ratio [C2H2]0/[OH]0 was in the range of 2.3 to 13.2 in the first set, and 14 to 125 (owing to greater hydroxyl detection sensitivity) in the second set. Values of the second-order rate coefficient obtained were nk5 = (2.9 ± 0.3) × 10−13 cm3/molec-sec in the first set, and nk5 = (2.1 ± 0.6) × 10−13 cm3/molec-sec in the second set, where n is the stoichiometric coefficient of OH. A value of the bimolecular rate constant k5 = (2.0 ± 0.6) × 10−13 cm/molec-sec is consistent with both sets of data, as well as an earlier determination.