Kinetic studies on the N(D-2,P-2)+CH4 and CD4 reactions: The role of nonadiabatic transitions on thermal rate constants

Thermal rate constants for the N(D-2,P-2) + CH4 (CD4) reactions have been m easured using a technique of pulse radiolysis-resonance absorption in the t emperature range between 223 and 298 EC. Activation energies determined fro m the temperature dependence were about 1.5 and 1.0 kcal/mol for the reacti ons of N(D-2) and N(P-2), respectively. The H/D kinetic isotope effects wer e about 1.8 and 1.6 for N(D-2) and N(P-2), respectively. The rate constants for N(P-2) + CH4 were much smaller than those for N(D-2) by a factor of 40 -60. Variational transition-state theory calculations of the rate constants for the N(D-2) + CH4 (CD4) insertion reaction have been carried out using the reaction path information obtained from ab initio molecular orbital cal culations. The comparison between the calculated and experimental rate. con stants shows that multiple surface coefficients are larger than the statist ical value, meaning that nonadiabatic transitions are important for the N(D -2) + CH4 reaction.