Theoretical calculations of thermal rate constants for the N(2D)+acetylene reaction

Variational transition-state theory calculations have been carried out for the N(2D)+C2H2 and C2D2 reactions using the results of ab initio molecular orbital calculations. Comparison between the calculated and experimental rate constants indicates that multiple surface coefficient is much larger than the value predicted from electronic degeneracy, meaning that non-adiabatic transitions are important for these reactions. We have calculated five doublet potential energy curves that asymptotically correlate to the N(2D)+C2H2 reactants in the long-range Van der Waals region, where the potential curves are close in energy. This result qualitatively suggests that non-adiabatic transitions effectively take place in the long-range region.