Abstract
The reactions of the cyclic molecules C6H6 (benzene), c-C3H6 (cyclopropane) and c-C6H12 (cyclohexane) with ArH+ (ArD+), H3+, N2H+, CH5+, HCO+, OCSH+, C2H3+, CS2H+ and H3O+ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C2H3+ proceed via proton transfer and all are fast except the H3O+ and CS2H+ reactions with c-C6H12 which are endothermic and which establish that the proton affinity of c-C6H12 is 160 ± 1 kcal mol−1, which is considerably lower than the published value. In the c-C3H6 and the c-C6H12 reactions multiple products are observed and hence “breakdown curves” for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C2H3+ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.