B. A. McGuire, A. M. Burkhardt, S. V. Kalenskii, C. N. Shingledecker, A. J. Remijan, E. Herbst, and M. C. McCarthy
reported on the
Detection of the Aromatic Molecule Benzonitrile, //c//-C₆H₅CN, in the Interstellar Medium
Science 359, 202–205 (2018).
The molecule, also known as phenyl cyanide, was detected first by stacking of rotational transitions observed in archival Nobeyama 45 m data. It was the only molecule out of a dozen cyclic molecules searched for that was detected by this method. Subsequently, attempts were made to detect individual transitions with the GBT 100 m telescope by covering a total of 1.875 GHz in the 18 to 23 GHz region. Nine transitions with J' = 7 to 9 and K_a =  0 to 2 were detected with modest to fairly good signal-to-noise ratios. Some of these transitions displayed partially resolved ¹⁴N hyperfine structure. The inferred column density is somewhat lower than that of HC₉N, the largest unambigously detected cyanopolyyne thus far.
NRAO issued a press release which was also issued by the CfA.
The molecule was the most promising candidate for the detection of a benzene derived aromatic molecule by means of radio astronomy. Was it surprising that it was found in TMC-1 ?

A. M. Burkhardt, R. A. Loomis, C. N. Shingledecker, K. L. K. Lee, A. J. Remijan, M. C. McCarthy, and B. A. McGuire
reported on the
Ubiquitous aromatic carbon chemistry at the earliest stages of star formation
Nat. Astron. 5, 181–187 (2021).
Benzonitrile was detected by the same method as in the first reference toward four additional dark clouds, Serpens 1A, 1B, 2, and L1521F. The HC₇N/c-C₆H₅CN ratio was found to be around 5 for the first threre sources and ~17 for L1521F. The last value is very similar to the one in TMC-1 derivewd from the previous entry.

V. M. Rivilla, D. San Andrés, M. Sanz-Novo, L. Colzi, I. Jiménez-Serra, A. López-Gallifa, A. Martínez-Henares, A. Megías, S. Martín, B. Tercero, S. Zeng, J. Loreau, M. Ben Khalifa, M. A. Requena-Torres and P. de Vicente
announced
Aromatic Rings in the Central Molecular Zone: Benzonitrile
Astron. Astrophys. 712, Art. No. A128 (2026).
The molecule was detected in two kinetically warmer, rotationally cold clouds G+0.693−0.027 and G+0.633−0.0604 close to the Galactic center in the course of molecular line surveys with the Yebes 40 m dish. The HC₇N/c-C₆H₅CN ratios of ~2.15 and ~2.4 are even lower than the values reported earlier. Additional values of comparison are given from other publications, including a value of ~30 in Lupus-1A.

Contributor(s): H. S. P. Müller; 01, 2018; 04, 2021; 08, 2026