Quadrupole structure in the rotational spectrum of the v8=1 and 2 and ground vibrational levels of CH3C14N for the frequency range 17–56 GHz

The rotational spectra in the ground and v8=1 and 2 vibrational states of methyl cyanide have been determined in the frequency range 17–56 GHz. Molecular constants for these vibrationally excited states have been determined from more than 30 observed rotational transitions. Experimentally measured frequencies are presented and compared with those calculated using the results of basic perturbation theory. Constants were obtained for the v8=1 level and these, along with the ground constants, used to generate constants for components of the v8=2 vibration. A model was developed for the quadrupole splitting for the ground and v8=1 levels. From these values spectral components were predicted and assigned for the higher vibration v8=2.