HOLGER S. P. MÜLLER, I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany; B. J. DROUIN, J. C. PEARSON, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA; A. BELLOCHE, K. M. MENTEN, Max-Planck Institut für Radioastronomie, 53121 Bonn, Germany.
Methyl cyanide, CH3CN, is an important interstellar molecule, in particular in hot and dense molecular cores, and it may play a role in the atmospheres of planets or of Titan. Therefore, we have recorded extensive rotational spectra up to 1.6~THz. Ground state rotational transitions of a number of minor isotopologs could be identified up to 1.2~THz in natural isotopic composition, including CH2DCN and 13CH3 13CN.
Recently, we have analyzed the rotational spectra of 13CH3CN, CH3 13CN, and CH3C15N in their v8 = 1 excited vibrational states from spectra covering most of the frequencies between 0.44~THz and 1.20~THz. The analyses of the 15N and 13C species were facilitated by previous data up to 144~GHz and 56~GHz, respectively. Spectroscopic parameters determined in the fits will be compared with those of the main isotopolog. The importance of these results, in particular for radio-astronomical observations with the Atacama Large Millimeter Array (ALMA), will be stressed by the detection of transitions pertaining to the 13C species in Sagittarius~B2(N).