Collisional stabilization of highly vibrationally excited o-, m- and p-xylene ions (C8H10+) from 300-900 K and 1-250 Torr

Branching ratios for the reactions of O-2(+) with all three xylene isomers have been measured as a function of temperature over a wide range (300-900 K) at a fixed number density (1.45 x 10(16) molecule cm(-3) of helium) and for in-xylene over an extended buffer gas pressure (50-250 Torr of nitrogen) and temperature (473-623 K) range. Rate constants measured under selected conditions indicate that the reactions proceed at the collisional rate. Two main products were observed in each reaction: the stabilized parent ion, C8H10+ (S) and a dissociative charge transfer product, C7H7+ (D). The ratio of S/D was found to vary significantly with both temperature and pressure. At high pressure very little dissociation occurred. Results of statistical modeling similar to that used in our studies of n-alkylbenzenes represent the data well. (c) 2005 Elsevier B.V. All rights reserved.