Thermal rate constants for R+N2H2→RH+N2H (R=H, OH, NH2) determined from multireference configuration interaction and variational transition state theory calculations

Abstract

Ab initio electronic structure calculations were performed to determine features of the potential energy surface for abstraction of a hydrogen atom from N2H2 by H, OH, and NH2. Based on multireference configuration interaction calculations with basis sets up to correlation consistent polarized valence triple zeta, the barrier heights determined for these reactions are 4.3, 3.0, and 4.4 kcal/mol, respectively. Using features of the potential energy surface along minimum energy paths determined at the complete active space self-consistent-field level of theory, variational transition state theory calculations were performed to determine the rate coefficients over the temperature range 300–3000 K. The temperature dependent computed rate coefficients for the three reactions are well represented by the following three-parameter expressions: kH(T) =1.41×10−19T2.63 exp(115.8/T) cm3 molec−1 s−1, kOH(T)=9.84×10−23 T3.40 exp(686.3/T) cm3 molec−1 s−1, and kNH2(T)=1.46×10−25T4.05 exp(810.5/T) cm3 molec−1 s−1. Abstraction from N2H2 is predicted to occur at a significantly slower rate than analogous abstractions from the isoelectronic HNO.