AB-INITIO STUDY OF THE ACTIVATION OF AMMONIA BY CO+

Mechanistic aspects of the reaction of Co+ with ammonia are investigat ed by ab initio calculations. The potential energy surface is explored at the CASSCF level. Relative stabilities of the various stationary p oints on the reaction path are obtained by applying the CASPT2 techniq ue. Binding energies for the reaction products CoNH3+, CoNH2+, and CoH + are calculated to be 52.1, 66.7, and 51.5 kcal/mol, respectively. Th ey correspond reasonably well with the relevant experimental values of 58.8 +/- 5, 61.3 +/- 2, and 46.6 +/- 2 kcal/mol, respectively, fallin g just a few kcal/mol outside the error bars of the measurements. The HCoNH2+ isomer of the CoNH3+ adduct is confirmed to represent a local minimum on the potential energy surface. It is separated from the addu ct by an energy barrier of 15 kcal/mol, and its formation from the rea ctants is just slightly exothermic by a few kcal/mol. The H-2 eliminat ion is experimentally not observed as a consequence of a complex tight four center transition state at about 58 kcal/mol above the ground st ate asymptote. The CoNH2+ and CoH+ exit channels are energetically sit uated below this barrier. Due to the high threshold energy, both react ion products are formed directly by simple N-H bond fission without HC oNH2+ acting as an intermediate.