AB-INITIO STUDY ON THE REACTION 2NH(X-3-SIGMA(-))-]NH2((X-B-2(1))-4)(N(S)

The geometries of the stationary points of the reaction 2NH(X (3) Sigm a(-)) -->NH2((XB1)-B-2) + N(S-4) have been optimized at the UHF, UMP2, and UMP4(SDQ) levels with polarized double and triple zeta basis sets . The best calculation of the potential barrier for this reaction is 6 .4 kcal/mol, obtained with the UMP-SAC4 theory. The intrinsic reaction coordinate (IRC) and vibrational frequencies along the IRC were calcu lated at the UMP2/6-311G* level, and the UMP2 energy profile was refi ned with the UQCISD(T) and UMP-SAC4 levels of theory. Theoretical rate constants calculated by conventional and variational transition state theories are in good agreement with the experimental values in the av ailable temperature range. (C) 1997 Elsevier Science B.V.