===== On the Detection of Methyl Isocyanide, CH3NC, in Space =====

J. Cernicharo, C. Kahane, M. Guélin, and J. Gomez-Gonzalez\\
reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1988A&A...189L...1C|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 CH<sub>3</sub>CN to CH<sub>3</sub>NC ratio of ∼30 is derived if slight opacity of CH<sub>3</sub>CN, as judged by lines of CH<sub>3</sub><sup>13</sup>CN, is taken into account.\\
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A. J. Remijan, J. M. Hollis, F. J. Lovas, D. F. Plusquellic, and P. R. Jewell\\
studied\\
**[[https://doi.org/10.1086/432908|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 CH<sub>3</sub>NC near 20.11 GHz and of CH<sub>3</sub>CN 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 CH<sub>3</sub>CN is neglected.\\
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P. Gratier, J. Pety, V. Guzmán, M. Gerin, J. R. Goicoechea, E. Roueff, and A. Faure\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/201321031|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 CH<sub>3</sub>NC to CH<sub>3</sub>CN ratio was ≈ 0.16.\\
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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\\
**[[https://doi.org/10.1051/0004-6361/201833140|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 CH<sub>3</sub>CN to CH<sub>3</sub>NC ratio is about 200 toward source B and more than 5000 toward source A.\\
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J. D. Tennis, C. Xue, D. Talbi, P. B. Changala, M. L. Sita, B. McGuire, and E Herbst\\
announced the\\
**[[https://doi.org/10.1093/mnras/stad2398|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 CH<sub>3</sub>CN near 18.40 GHz was also detected and a CH<sub>3</sub>CN : CH<sub>3</sub>NC ratio of ~17 was inferred.\\
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Contributor(s): H. S. P. Müller 08, 2018; 09, 2023

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