Rotational and rovibrational spectroscopy of the v 8 = 1 and 2 vibrational states of CH3NC

Abstract

The lowest frequency vibration–rotation band ν 8, corresponding to the degenerate CNC bending vibration of methyl isocyanide (CH3NC) with band center at 267.3 cm−1, was studied by FTIR spectroscopy between 215 and 320 cm−1 and rotational spectroscopy in the range from 201 to 383 GHz in order to describe the vibration–rotation dynamics with the inclusion of all important anharmonic and vibration–rotation interactions. Assignments extended to higher-K rotational states in both vibration–rotation and rotational spectra reveal a resonance crossing with the v 8 = 2 overtone level due to a local anharmonic Fermi resonance. The simultaneous analysis of both types of data provides a fully quantitative reproduction of the experimental data as well as a preliminary characterization of the v 8 = 2 level. The parallel component of the overtone band with band center at 524.6 cm−1 was assigned for the first time from spectra in the region from 480 to 585 cm−1 together with the hot bands in the region of the fundamental band.