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

The rate coefficients and product ion branching ratios have been determined for reactions between NO+ and three ketones, acetone, 2-butanone, and 3-pe ntanone, as a function of NO+/reactant ketone centre-of-mass energy, E-r, a nd NO+/helium carrier gas atom centre-of-mass energy, E-c, in a flowing aft erglow selected ion flow drift tube apparatus. In these experiments, the he lium carrier gas was maintained at a temperature of 300 K. At zero drift fi eld, association was the dominant channel occurring at close to the collisi on 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 th e association rate coefficient with increasing E-c exhibits an inverse powe r law dependence k(3) proportional to E-c(-n) where n similar to 2.5 for al l three ketones. This dependence is much larger than predicted by simple th eory and may be indicative of low energy vibrations contributing to the tot al energy pool in the (NO. ketone)(+*) excited complex. (Int J Mass Spectro m 193 (1999) 35-43) (C) 1999 Elsevier Science B.V.