Study of the HCCNC and HNCCC isotopologs in TMC-1

We present the detection of the three 13C isotopologs of HCCNC and HNCCC toward TMC-1 using the QUIJOTE line survey. In addition, the D species has also been detected for these two isomers of HCCCN, whereas the 15N isotopolog was only detected for HCCNC. Using high-J lines of HCCNC and HNCCC, we were able to derive very precise rotational temperatures, column densities, and subsequently the isotopic abundance ratios. We found that 12C/13C is around 90 for the three possible substitutions in both isomers. These results are slightly different from what has been found for the most abundant isomer HCCCN, for which abundances of 105, 95, and 66 were found for each one of the three possible positions of 13C. The H/D abundance ratio was found to be 31+/-4 for HCCNC and of 53+/-6 for HNCCC. The latter is similar to the H/D abundace ratio derived for HCCCN (59). The 14N/15N isotopic abundance ratio in HCCNC is 243+/-24.
Comment: Accepted as a Letter in Astronomy & Astrophysics on 22 January 2024