Implication of Formation Mechanisms of HC5N in TMC-1 as Studied by 13C Isotopic Fractionation

TL;DR

This study investigates the formation mechanisms of HC5N in TMC-1 by analyzing 13C isotopic fractionation, revealing isotopologue ratios that suggest specific chemical pathways in the molecular cloud.

Contribution

It provides new observational data on 13C isotopologues of HC5N and discusses implications for its formation mechanisms in interstellar environments.

Findings

Detected five 13C isotopologues with high signal-to-noise ratios.

Found isotopologue abundance ratios close to unity, indicating uniform formation pathways.

Determined an average HC5N/13C ratio of 94, slightly above the local interstellar 12C/13C ratio.

Abstract

We observed the J = 9-8 and 16-15 rotational transitions of the normal species and five 13C isotopologues of HC5N to study its formation mechanisms toward the cyanopolyyne peak in Taurus Molecular Cloud-1, with the 45-m radio telescope of Nobeyama Radio Observatory. We detected the five 13C isotopologues with high signal-to-noise ratios between 12 and 20, as well as the normal species. The abundance ratios of the five 13C isotopologues of HC5N are found to be 1.00:0.97:1.03:1.05:1.16 (0.19) for [H13CCCCCN]:[HC13CCCCN]:[HCC13CCCN]:[HCCC13CCN]:[HCCCC13CN]. We do not find any significant differences among the five 13C isotopologues. The averaged [HC5N]/[13C isotopologues] abundance ratio is determined to be 94 (6), which is slightly higher than the local interstellar elemental 12C/13C ratio of 60-70. Possible formation pathways are discussed on the basis of these results.