Kinetic studies of the reactions of CN radicals with alkanes in the temperature range between 294 and 1260 K

Abstract

Absolute rate coefficients for the reaction of CN radicals with methane (κ 1), ethane (κ 2) and propane (κ 3) were measured as a function of temperature in a heatable quartz reactor by means of a laser photolysis/laser-induced fluorescence (LP/LIF) technique. CN was generated by 193 nm photolysis of cyanogen. No pressure dependence was found for any of the reactions between 300 and 5000 Pa. In the case of reactions with ethane and propane, rate coefficients were also measured for CN(ν=1). No significant change κ 2 and κ 3 with increasing vibrational energy of the CN molecule was noticeable. The temperature dependences of the rate constants are described by the following expressions: κ 1 (298⩽ T⩽1267 K)=(1.25±0.1)×10 5 T (2.64±0.2)×exp [(78±8) K/ T] cm 3 mol −1 s −1; κ 2(294⩽ T⩽984 K)=(2.25±0.1)×10 5 T (2.7±0.2) exp[(810±80) K/ T] cm 3 mol −1s −1; κ 3(294⩽ T⩽721 K)=(2.33±0.2)×10 11 T (0.81±0.1)exp[(109±9) K/ T] cm 3 mol −1 s −1.