THEORETICAL-STUDY OF INTERMEDIATE COMPLEXES AND THE SADDLE-POINT FOR NH3+OH -] NH2+H2O

Ab initio molecular orbital theory was used to study parts of the potential energy surface of the hydrogen abstraction reaction between ammonia and the hydroxyl radical. Optimized geometries and harmonic vibrational frequencies were calculated at the MP2/6-31G(d,p) level of theory, and energy changes were calculated at the MP4/6-311+G(d,p) level with spin projection and at the QCI/6-311+G(2df,p) level. Three stationary points on the potential energy surface were located. A very weak hydrogen-bonded complex (HBR) was found close to the reactants. Then, a saddle point (SP) was located with energy slightly above that of the reactants. The third stationary point was located close to the products (HBP) and is lower in energy than they are. The effects of spin projection, the method of calculation, and thermal corrections (TC) were analyzed.