MCSCF reaction-path energetics and thermal rate-constants for the reaction of³NH with H₂

The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (³∑^-)+H₂ (¹∑_g⁺) → NH₂ (²B₁)+H (²S) involving the lowest triplet electronic state of NH₃ were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol^-1 agrees with the experimental value within 2 kcal mol^-1. The barrier to reaction is 23.4 kcal mol^-1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H₂, whereas those of the reverse reaction are by a factor of 20 larger than those of OH₂ with H.