2016A&A...586A..17M

Methyl cyanide is an important trace molecule in space, especially in star-forming regions where it is one of the more common molecules used to derive kinetic temperatures. We want to obtain accurate spectroscopic parameters of minor isotopologs of methyl cyanide in their lowest excited v₈=1 vibrational states to support astronomical observations, in particular, with interferometers such as ALMA. The laboratory rotational spectrum of methyl cyanide in natural isotopic composition has been recorded from the millimeter to the terahertz regions. Transitions with good signal-to-noise ratios could be identified for the three isotopic species CH₃¹³CN, ¹³CH₃CN, and CH₃C¹⁵N up to about 1.2 THz (J''≤66). Accurate spectroscopic parameters were obtained for all three species. The present data were already instrumental in identifying v₈=1 lines of methyl cyanide with one ¹³C in IRAM 30m and ALMA data toward Sagittarius B2(N).