THE SUBMILLIMETER-WAVE SPECTRUM OF ISOTOPIC METHYL CYANIDE

The laboratory submillimeter wave rotational spectrum of the (CH3CN)-C -13, (CH3CN)-C-13, and (CH3CN)-N-15 isotopomers of methyl cyanide has been observed in natural abundance in the 294 to 607 GHz region. The m aximum J and K values are 34 and 14, respectively. Fifteen additional CH3CN transitions up to K = 21 were also measured. The transitions of all four species are fitted to a symmetric top Hamiltonian, and the ro tation and distortion constants are determined. The N-14 quadrupole an d spin rotation coupling constants are also calculated and presented. Suggested values for many other parameters, which could not be directl y determined from the isotope spectra, are calculated from the normal species values and isotope relationships. The determined and calculate d constants should predict the spectrum of the three isotopomers to we ll over 1 THz accurately enough for astronomical assignments.