Methyl isocyanide. Spectroscopic studies of isotopically substituted species, and the general harmonic potential function

Abstract

Infrared gas phase spectra of CH3NC, 13CH3NC, CH315NC, CH3N13C, CD3NC, 13CD3NC, and CD315NC have been studied in detail, in order to determine accurate fundamental vibration frequency displacements on heavy isotopic substitution and Coriolis interaction constants for the degenerate fundamental vibrations. These data, along with the fundamental frequencies of CH3NC and CD3NC and centrifugal distortion constants for six isotopic species, form a self-consistent set of 105 data, which enable all 20 parameters of the general harmonic potential function of methyl isocyanide to be determined within narrow limits. Comparison with the predictions of ab initio calculations reveals disagreement in the values of three interaction constants, apparently well outside experimental error. Undetermined centrifugal distortion and Coriolis interaction constants are calculated for CH3NC and CD3NC to assist in future spectroscopic studies.