K. Kawaguchi, S. Takano, M. Ohishi, S.-I. Ishikawa, K. Miyazawa, N. Kaifu, K. Yamashita, S. Yamamoto, S. Saito, Y. Ohshima, and Y. Endo
reported on the
Detection of HNCCC in TMC-1
Astrophys. J. 396, L49 (1992).
The Nobeyama 45 m telescope was used to detect the J = 3 – 2, 4 – 3, and 5 – 4 transitions near 28.0, 37.3, and 46.7 GHz. The HCCNC isomer was found only slightly earlier, whereas the HC₃N isomer had been known for a considerable time.

P. D. Gensheimer reported on
Observations of HCCNC and HNCCC in IRC+10216
Astrophys. Space Sci. 251, 199 (1997).
The NRAO 12 m telescope was used to detect the J = 11 – 10 transition near 102.7 GHz. The HCCNC to HNC₃ ratio is about 8, similar to that in TMC-1. Because of only one detected line, this report should be viewed with some caution.

C. Vastel, K. Kawaguchi, D. Quénard, M. Ohishi, B. Lefloch, R. Bachiller, and H. S. P. Müller
used the IRAM 30 m telescope for
High Spectral Resolution Observations of HNC₃ and HCCNC in the L1544 Pre-stellar Core
Mon. Not. R. Astron. Soc. 474, L76 (2018).
The J = 8 – 7, 9 – 8, and 10 – 9 transitions were detected near 74.7, 84.0, and 93.4 GHz. The column density is only slightly smaller than that in TMC-1, similar to HCCNC, even though HC₃N is less abundant by about one order of magnitide in L1544 compared to TMC-1.

J. Cernicharo, N. Marcelino, M. Agúndez, C. Bermúdez, C. Cabezas, B. Tercero, and J. R. Pardo
reported on the
Discovery of HC₄NC in TMC-1: A study of the isomers of HC₃N, HC₅N, and HC₇N
Astron. Astrophys. 642, Art. No. L8 (2020).
The authors report the detection of DNC₃. The observations were obtained with the Yebes 40m radio telescope in the course of a line survey covering 31.0–50.3 GHz.

J. Cernicharo, B. Tercero, C. Cabezas, M. Agúndez, E. Roueff, R. Fuentetaja, N. Marcelino, and P. de Vicente
carried out more recently a
Study of the HCCNC and HNCCC isotopologs in TMC-1
Astron. Astrophys. 682, Art. No. L13 (2024).
They reported in the framework of improved data of the above survey the detection of the three HNC₃ ¹³C isotopomers. They determined the ¹²C/¹³C ratios of ~90 with scatter that is insignificant with respect to the uncertainties. These values are somewhat lower than ~65 usually found in the the local ISM, but very similar to values of HCCNC ¹³C isotopomers and to two of the three HC₃N ¹³C isotopomers. In addition, an H/D ratio of ~53 was reported, similar to the value of 57 ± 2 of HC₃N.

Contributor(s): H. S. P. Müller; 12, 2017; 11, 2020; 04, 2024