15min:

VANESSA A. CASTLEBERRY, S. JASON DEE, OTSMAR J. VILLARROEL, IVANNA E. LABOREN, SARAH E. FREY AND DARRIN J. BELLERT, Department of Chemistry and Biochemistry, Baylor University, Waco, Texas, 76798.

A unique application of a custom fabricated photodissociation spectrometer permits the determination of thermodynamic properties (activation energies), reaction rates, and mechanistic details of bare metal cation mediated C-C -bond activation in the gas phase. Specifically, the products and rates resulting from the unimolecular decomposition of the Ni⁺Acetone (Ni⁺Ac) adduct are monitored after absorption of a known amount of energy. The three dissociative products which are observed in high yield are Ni⁺, Ni⁺CO, and CH3CO⁺. The latter two fragment ions result from the activation of a C-C -bond. It was found that minimally 14 000 cm^-1 of energy must be deposited into the adduct ion to induce C-C bond breakage. Preliminary results for the Ni⁺ activation of the C-C -bond of acetone indicate that there are (at least) two low energy reaction coordinates leading to C-C bond breakage. The lower energy pathway emerges from the doublet ground state with an upper limit to the activation energy of 14 000 cm^-1 and reaction rate ~0.14 molecules/µs. The higher energy path is assumed to be along the quartet reaction coordinate with a minimum activation energy of 18 800 cm^-1 (relative to the ground state) and a slightly slower reaction rate.