ENERGY AND RATE DETERMINATIONS TO ACTIVATE THE C-C $\sigma$-BOND OF ACETONE BY GASEOUS $NI^+$

Abstract

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 $\sigma$-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 $\sigma$-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 $\sigma$-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 $\approx$0.14 molecules/$\mu$s. The higher energy path is assumed to be along the quartet reaction coordinate with a minimum activation energy of 18 800 cm$^{-1}$ (relative to the ground state) and a slightly slower reaction rate.