Competitive association and charge transfer in the reactions of NO + with some ketones: a selected ion flow drift tube study

Abstract

The rate coefficients and product ion branching ratios have been determined for reactions between NO + and three ketones, acetone, 2-butanone, and 3-pentanone, as a function of NO +/reactant ketone centre-of-mass energy, E r , and NO +/helium carrier gas atom centre-of-mass energy, E c , in a flowing afterglow selected ion flow drift tube apparatus. In these experiments, the helium carrier gas was maintained at a temperature of 300 K. At zero drift field, association was the dominant channel occurring at close to the collision rate forming NO · + ketone adduct ions. At higher drift fields ( E r , E c < 1 eV), charge transfer and dissociative charge transfer channels became the major channels forming fragment ions of the ketones. The decrease in the association rate coefficient with increasing E c exhibits an inverse power law dependence k 3 ∝ E c − n where n ∼ 2.5 for all three ketones. This dependence is much larger than predicted by simple theory and may be indicative of low energy vibrations contributing to the total energy pool in the (NO · ketone) +∗ excited complex. Keywords: Ion/molecule association; SIFT; Drift tube; Charge transfer