Chemistry of HCNH~+:mechanisms, structures, and relevance to Titan's atmosphere

摘要

The chemistry of HCNH~+ in Titan's atmosphere is not completely understood despite previous experimental and theoretical studies. In response to recent suggestions in the literature, we have searched for specific products of the reactions of HCNH~+ with H_2, CH_4, C_2H_2, and C_2H_4 using the flowing afterglow-selected ion flow tube technique. We have probed for an association mechanism for reaction with H_2, and associative-H_2 loss for the reactions involving CH_4, C_2H_2, and C_2H_4. In all cases, these reaction mechanisms were found to be inefficient pathways for the depletion of HCNH~+. Our ab initio computational studies characterize the structures and energies for these mechanisms and indicate that the proposed pathways are endothermic or possess reaction barriers. We compare our studies to previous experimental and computational work, and we suggest other ion-neutral reactions with HCNH? that have not been included in previous models of Titan's ionosphere.