Kinetics of CN reactions with allene, butadiene, propylene and acrylonitrile

Abstract

The two-laser pump-probe technique has been used to study the kinetics of the reaction of CN radicals with C 3H 6, CD 3C 2H 3, C 3D 6, C 2H 3CN, C 3H 4 and C 4H 6 at temperatures between 297 and 740 K. CN was generaged by 248-nm photolysis of ICN. Laser-induced fluorescence of the CN radical has been used for its detection by CN (B←X) excitation. The values for the rate constants, given in units of cm 3/s, are reported as: k(C 3H 6)=10 −9.88±0.10exp(+244±96.3/ T), k(C 3H 3D 3) = 10 −9.76±0.04 exp (+143.4±35.1/ T), k(C 3D 6)=10 −9.87±0.05exp(+231.4±47.01/ T, k(C 2H 3CN)=10 −10.52±0.02exp(+103.6±20.3/ T), k(C 3H 4)=10 −9.58±0.08 ×exp(+167.4±73.7/ T), k(C 4H 6)=10 −9.59±0.04exp(+169.2±33.1/ T). The absolute rates of CN reactions with CH 3CHCH 2, CD 3CHCH 2 and CD 3CDCD 2 are essentially the same and are somewhat faster than that of the CN+C 2H 4 reaction. This suggests that the CN+C 3H 6 reaction occurs primarily by addition to the unsaturated bond and the CH 3 group enhances the addition process slightly. The rate of the CN+CH 2CHCN reaction, however, was found to be a factor of six slower than that of CN+C 2H 4, indicating a substantial electron withdrawing effect of the CN group in vinyl cyanide which results in the reduction in the addition rate. The rates for CN reaction with CH 2CCH 2 and CH 2CHCHCH 2 are approximately the same and are twice that of CN+C 2H 4.