Assignment of methyl cyanide FIR laser lines

Abstract In the literature, there are measurements for more than 30 FIR laser emissions of the CH 3 CN molecule, and in addition observations of 13 lines for the deuterated species CD 3 CN. For many lines the assignments have been proposed, but these are often based on old and relatively inaccurate infrared spectra. Starting from a recent series of high resolution FTIR studies of these molecules in our laboratory, the assignments of these FIR laser lines have been studied. For CH 3 CN, accurate combination loops confirmed 14 previous assignments and checked seven new ones. In addition, a new idea for three lines has been provided. For CD 3 CN, four old assignments has been confirmed. Five new detailed explanations and two new tentative possibilities are presented here.