Ab initio study on the reaction 2NH(2)-> NH+NH3

摘要

The geometries of the reactant, products, and transition state of the title reaction were optimized at the UHF and UMP2 levels with the double and triple zeta basis sets as well as polarization functions by using the energy-gradient method. The potential-energy barrier for this reaction is 3.73 kcal/mol at the UMP-SAC4 level of theory. The intrinsic reaction coordinate (IRC) was performed at the UMP2/6-311G** level. The changes of the geometry and the bound vibrational modes along the IRC were analyzed. To obtain a more reliable potential-energy curve for the study of the reaction dynamics, the UMP2 energy profile was refined along the IRC with the UQCISD(T) and UMP-SACC levels of theory. The theoretical rate constants calculated by the conventional and the variational transition-state theories at the UMP-SAC4 level agree approximately with the experimental values in the high-temperature range from 2000 to 3000 K and are not affected by the variation and quantum effects. (C) 1998 John Wiley & Sons, Inc. [References: 21]