KINETICS OF CN REACTIONS WITH ALLENE, BUTADIENE, PROPYLENE AND ACRYLONITRILE

The two-laser pump-probe technique has been used to study the kinetics of the reaction of CN radicals with C3H6, CD3C2H3, C3D6, C2H3CN, C3H4 and C4H6 at temperatures between 297 and 740 K. CN was generated 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 cm3/s, are reported as: k(C3H6) = 10(-9.88+/-0.10) exp (+244+/-96.3/T), k(C3H3D3) = 10(-9.76+/-0.04) exp (+143.4+/-35.1/T), k(C3D6) = 10(-9.87+/-0.05) exp (+231.4+/-47.01/T), k(C2H3CN) = 10(-10.52+/-0.02) exp (+103.6+/-20.3/T), k(C3H4) = 10(-9.58+/-0.08) x exp (+167.4+/-73.7/T), k(C4H6) = 10(-9.59+/-0.04) exp (+169.2+/-33.1/T). The absolute rates of CN reactions with CH3CH=CH2, CD3CH=CH2 and CD3CD=CD2 are essentially the same and are somewhat faster than that of the CN+C2H4 reaction. This suggests that the CN+C3H6 reaction occurs primarily by addition to the unsaturated bond and the CH3 group enhances the addition process slightly. The rate of the CN+CH2=CHCN reaction, however, was found to be a factor of six slower than that of CN+C2H4, 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 CH2=C=CH2 and CH2=CHCH=CH2 are approximately the same and are twice that of CN+C2H4.