J. Cernicharo, C. Kahane, M. Guélin, and J. Gomez-Gonzalez
reported on the
Tentative Detection of CH₃NC towards Sgr B2
Astron. Astrophys. 189, L1–L2 (1988).
The authors searched for methyl isocyanide, also known as isocyanomethane, toward Sgr B2(OH) with the IRAM 30 m telescope. The blended K = 0 and 1 components of the J = 4 – 3, 5 – 4, and 7 – 6 transitions near 80.42, 100.53, and 140.73 GHz were tentatively identified as emission features. Assuming the identification is correct, a CH₃CN to CH₃NC ratio of ∼30 is derived if slight opacity of CH₃CN, as judged by lines of CH₃¹³CN, is taken into account.

A. J. Remijan, J. M. Hollis, F. J. Lovas, D. F. Plusquellic, and P. R. Jewell
studied
Interstellar Isomers: The Importance of Bonding Energy Differences
Astrophys. J. 632, 333–339 (2005).
The 100 m GBT was used to carry out observations toward Sgr B2(N). The J = 1 – 0 transitions of CH₃NC near 20.11 GHz and of CH₃CN near 18.40 GHz were observed in absorption toward the Large Molecule Heimat, Sgr B2(N1), +64 km/s component and in emission toward Sgr B2(N2), the +73 km/s component. The ratios are about 1 : 20 and 1 : 40, respectively, if potential opacity of CH₃CN is neglected.

P. Gratier, J. Pety, V. Guzmán, M. Gerin, J. R. Goicoechea, E. Roueff, and A. Faure
reported on
The IRAM-30 m line survey of the Horsehead PDR III. High abundance of complex (iso-)nitrile molecules in UV-illuminated gas
Astron. Astrophys. 557, Art. No. A101 (2013).
The K = 0, 1, and 3 transitions of J = 5 – 4 were detected with reasonable signal-to-noise ratio, the K = 2 line was on the edge. The CH₃NC to CH₃CN ratio was ≈ 0.16.

H. Calcutt, M. R. Fiechter, E. R. Willis, H. S. P. Müller, R. T. Garrod, J. K. Jørgensen, S. F. Wampfler, T. L. Bourke, A. Coutens, M. N. Drozdovskaya, N. F. W. Ligterink, and L. E. Kristensen,
reported on
The ALMA-PILS survey: First detection of methyl isocyanide (CH₃NC) in a solar-type protostar
Astron. Astrophys. 617 (2018), Art. No. A95.
Several transitions with J = 17 – 16 and 18 – 17 and K between 0 and 7 were detected near 342 and 362 GHz, respectively toward source B. The molecule was not detected toward source A. The CH₃CN to CH₃NC ratio is about 200 toward source B and more than 5000 toward source A.

J. D. Tennis, C. Xue, D. Talbi, P. B. Changala, M. L. Sita, B. McGuire, and E Herbst
announced the
Detection and Modelling of CH₃NC in TMC-1
Mon. Not. R. Astron. Soc. 525, 2154–2171 (2023).
The J = 1 − 0 transition near 20.105 GHz was detected in the course of the GOTHAM line survey toward TMC-1 with the 100 m GBT. The respective transition of CH₃CN near 18.40 GHz was also detected and a CH₃CN : CH₃NC ratio of ~17 was inferred.

Contributor(s): H. S. P. Müller 08, 2018; 09, 2023