The effect of N-heteroatoms and CH 3 substituents on dissociative electron–ion recombination of protonated single six membered ring compounds at room temperature

Abstract

Electron–ion dissociative recombination rate constants have been determined for protonated single six-membered hydrocarbon rings with varying N-atom substitution in the rings and varying degrees of methyl substitutions to the rings. The species studied have been protonated forms of the xylenes (C 8H 10; with configurations o, m, and p), the picolines (C 6H 7N; with methyl substitutions located at 2, 3, and 4), mesitylene (C 9H 12) and 2, 5-lutidine (C 7H 9N). By operating at high reactant vapor pressures, ternary association has been made to dominate over recombination to create proton bound dimers and the rate constants of these species have been determined. The studies were made at room temperature in a flowing afterglow with a Langmuir probe to determine the reduction in electron density as a function of distance along the flow tube. All of the data except for mesitylene showed a consistent trend with the numbers of N-atom substitutions and CH 3 attached to the rings. For the protonated species, the rate constants increase with the number of nitrogens and decreased with number of CH 3 substituents attached to the ring. For proton bound dimers, the rate constants increase with both, the number of N-atoms and number of CH 3 substituents. For the xylene and picoline isomer's the measurements showed that the rate constants were independent of isomeric form, and thus, it is not necessary to study all isomeric forms. The relevance of these studies to the ionosphere of Titan is discussed.