AMMONIA ACTIVATION BY CO+, NI+, AND CU+ - M+-NH2 BOND-ENERGIES AND M+=NH3 ADDUCT LIFETIMES

Reactions of Co+, Ni+, and Cu+ with ammonia are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. All three metal ions form MH+ and MNH2+ in endothermic reactions, but in contrast to reactions of Sc+, Ti+, and V+ with ammonia, no MNH+ formation is observed. Thresholds for the cross sections are interpreted to give the 298 K bond energies of D-degrees(Co+-NH2) = 2.66 +/- 0.09 eV, D-degrees(Ni+-NH2) = 2.41 +/- 0.08 eV, and D-degrees(Cu+-NH2) = 2.09 +/- 0.13 eV. Details of the bonding interaction between M+ and NH2 are discussed. At low kinetic energies, formation of MNH3+ is also observed and found to be a result of secondary stabilizing collisions. Lifetimes for these adducts are determined and compared to values calculated by RRKM theory. Dual features in the cross section for adduct formation in the reaction of Co+ with NH3 (and ND3) are shown to have drastically different lifetimes and are attributed to different structural isomers, Co+...NH3 and H-Co+-NH2.