MCSCF REACTION-PATH ENERGETICS AND THERMAL RATE-CONSTANTS FOR THE REACTION OF 3NH WITH H-2

The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (3SIGMA-) + H-2 (1SIGMA(g)+) --> NH2 (2B1) + H (2S) involving the lowest triplet electronic state of NH3 were calcula ted 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 cal culated 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 magnit ude smaller than those of the comparable reaction of OH with H-2, wher eas those of the reverse reaction are by a factor of 20 larger than th ose of OH2 with H.