Reactions of Ar+ with selected volatile organic compounds.: A flowing afterglow and selected ion flow tube study

Temperature-dependent rate coefficients and branching ratios for the reactions of Ar+ with a variety of volatile organic hydrocarbons are reported. Reactions of N-2(+) and CO2+ were undertaken to calibrate a newly constructed variable-temperature flowing afterglow (VTFA) complemented with a selected ion flow tube (SIFT). In addition, the first determinations of rate coefficients for the reaction of Ar+ with several organic hydrocarbons (toluene, pyridine, furan, thiophene, cyclohexene, cyclooctene, cyclohexane, and tetrahydrofuran) have been measured between 298 and 423 K with a VT-SIFT. Analogous to the Ar+ + C6H6 reaction, these reactions proceed by nondissociative and dissociative charge transfer, and very little temperature dependence is observed for the rate coefficients. At 298 K and 0.5 Torr, the rate coefficients are similar [(1.4-1.8) x 10(-9) cm(3)/s] for all of the Ar+ reactions with the organic hydrocarbons, except for pyridine (2.3 x 10(-9) cm(3)/s). These values are in reasonable agreement with rate coefficients predicted from average dipole orientation (ADO) theory. The degree of fragmentation appears to be loosely correlated to the difference in ionization potential between Ar+ and that of the neutral compounds as well as the degree of unsaturation of the hydrocarbon.