First detection of HC515N in the interstellar medium

Abstract

We report the first detection of HC 5 15 N with the J = 9-8 rotational line from the cyanopolyyne peak in Taurus Molecular Cloud-1 (TMC-1 CP) using the 45 m radio telescope of the Nobeyama Radio Observatory. The column density of HC 5 15 N is derived to be (1.9 ± 0.5) × 10 11 cm -2 (1σ). We apply the double-isotope method to derive the 14 N/ 15 N ratios of HC 5 N and HC 3 N in TMC-1 CP. The 14 N/ 15 N ratios are calculated to be 344 ± 53 and 257 ± 54 for HC 5 N and HC 3 N, respectively. The 14 N/ 15 N ratio of HC 5 N is lower than the elemental ratio in the local interstellar medium (∼440) and slightly higher than that of HC 3 N in TMC-1 CP. Since HC 3 N is formed via the neutral-neutral reaction between C 2 H 2 and CN, the slightly higher 14 N/ 15 N ratio of HC 5 N may support our previous suggestions that the main formation mechanism of HC 5 N is the ion-molecule reactions between hydrocarbon ions (C 5 Hn+) and nitrogen atoms.