Rate constants and branching ratios for the reactions of various positive ions with naphthalene from 300 to 1400 K

Abstract

Temperature dependent rate constants and branching ratios are reported for the reactions of a variety of ions with recombination energies ranging from 9.26 eV (NO+) to 21.56 eV (Ne+) with naphthalene. For most ions, the measurements are made between 300 and 370 K in a variable temperature-selected ion flow tube (VT-SIFT). For the reactions of Ar+ and N2/+, data have also been measured between 300 and 500 K in the selected ion flow tube. In addition, for the reactions of O2/+ and N2/+, data have been obtained between 500 and 1400 K in a high temperature flowing afterglow (HTFA). These are among the first determinations of branching ratios for ion-molecule reactions measured over 700 K. All reactions are found to proceed at the Langevin collision rate for all temperatures studied. The reactions proceed by nondissociative and dissociative charge transfer except for the reaction involving F+ where some of the reactivity is attributed to chemical channels. No dissociative charge transfer is observed for ions with recombination energies equal to or less than that for N2/+ at room temperature. At higher temperatures in the N2/+ reaction and for ions with higher recombination energies (F+ Ne+), naphthalene cation dissociation is observed, implying a threshold over 16 eV. This value is substantially higher than the known thermodynamic threshold because of kinetic shifts and quenching of the excited state of C10H8/+ by collisions with the helium buffer gas. The observed product thresholds and branching ratios are presented within the context of previous work and the implications for combustion chemistry are discussed. (C) 2000 Elsevier Science B.V.