J. Cernicharo, C. Kahane, M. Guélin, and J. Gomez-Gonzalez
reported on the
Tentative Detection of CH<sub>3</sub>NC 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
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 (CH<sub>3</sub>NC) 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 CH<sub>3</sub>NC 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

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