Abstract
Abstract We report the first detection of HC515N 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 HC515N is derived to be (1.9 ± 0.5) × 1011 cm−2 (1σ). We apply the double-isotope method to derive the 14N/15N ratios of HC5N and HC3N in TMC-1 CP. The 14N/15N ratios are calculated to be 344 ± 53 and 257 ± 54 for HC5N and HC3N, respectively. The 14N/15N ratio of HC5N is lower than the elemental ratio in the local interstellar medium (∼440) and slightly higher than that of HC3N in TMC-1 CP. Since HC3N is formed via the neutral–neutral reaction between C2H2 and CN, the slightly higher 14N/15N ratio of HC5N may support our previous suggestions that the main formation mechanism of HC5N is the ion–molecule reactions between hydrocarbon ions (C5H$_{n}^{+}$) and nitrogen atoms.
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