Searches for the Protonated Interstellar Species HC 3NH +, CH 3CNH +, and HOCS +: Implications for Ion-Molecule Chemistry

It is reported here that observed limits for the interstellar abundance ratios HC3NH(+)/HC3N, CH3CNH(+)/CH3CN, and HOCS(+)/OCS are consistent with current interstellar ion-molecule formation models, although the low abundance of HC3NH(+) precludes several reaction pathways for forming higher-order cyanopolyynes. It is also reported that HC3NH(+)/HC3N is at least 10 times smaller than HCNH(+)/CHN, a result that is not explainable solely by ion-molecule processes and that may suggest a non-gas-phase depletion mechanism for HCN such as absorption onto grains. There is no evidence for high-temperature HOCS(+)/OCS chemistry.