TEMPERATURE-DEPENDENCE OF THE REACTIONS OF CH RADICALS WITH NO, NH3 AND N2O IN THE RANGE 200-1300-K

Bimolecular rate constants for the reactions of CH(X2PI) radicals with nitric oxide, ammonia and nitrous oxide were measured under pseudo-first-order conditions at 4 Torr total pressure, as a function of temperature in the range 300-1300 K for the CH + NO and CH+NH3 reaction and in the range 200-1250 K for the CH+N2O reaction. CH radicals were generated by excimer laser photolysis of CHClBr2/Ar mixtures and were detected by laser-induced fluorescence. The rate constant of the reaction CH+NO was found to be independent of temperature. The measured rate constants of the reactions CH+N2O and CH+NH3 exhibit negative temperature dependences which are described by the following Arrhenius equations (with E(A) in units of kJ/mol): k(CH+N2O)(T) = (3.09 +/- 0.07) x 10(-11) exp[(2.14 +/- 0.08)/RT] cm3 s-1, k(CH+NH3) (T) = (7.23 +/- 0.17) x 10(-11) exp[(2.64 +/- 0.10)/RT] cm3 s-1 and kCH+NO(T) = (1.87 +/- 0.06) x 10(-10) exp[(0.00 +/- 0.15)/RT] cm3 s-1. All reactions were found to be very fast, with rate constants close to the ps kinetic limit. The negative temperature dependences for the reactions CH+N2O and CH+NH3 are in accord with an addition/decomposition mechanism and are similar to those observed for the reactions of CH radicals with saturated and unsaturated hydrocarbons.