Bimolecular reaction dynamics of Co +( 3F 4) + acetone reaction in real time

Abstract

A beam of Co +( 3F 4) is formed at a sharp zero of time by resonant two-photon ionization with a ns dye laser pulse and crossed with a beam of acetone gas under single collision conditions at collision energies E t = 0.01 eV and 0.23 eV. The ion-molecule reaction occurs in field-free space in the extraction region of a time-of-flight mass spectrometer. After a variable time delay t ext = 0.8 − 8 μs, a fast high voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe three product channels, formation of long-lived CoC 3H 6O + complexes and the two elimination products, CoCO + (+ C 2H 6) and CoC 2H 6 + (+ CO). The long-lived complexes decay to elimination products and back to Co + + acetone reactants on a wide range of time scales, as revealed by retarding field analysis of the metastable decay. Some complexes eliminate C 2H 6 on a 500 ns timescale, as revealed by tailing of the CoCO + peak. Other complexes still have not decayed on a 25 μs time scale. Deuteration of the acetone substantially decreases the elimination rates. We discuss how angular momentum conservation can lead to nonexponential complex decay and time-dependent product branching.