Fourier transform spectra and torsion–rotation structure of the CO-stretching 2 ν8 overtone and 2 ν8– ν8 hot band of CH 3OH

Abstract

The Fourier transform infrared (FTIR) spectrum of the 2 ν 8 overtone band of the CO-stretching vibrational mode of CH 3OH has been investigated in the 5-μm region at a spectral resolution of 0.0048 cm −1 (1/MOPD) and a higher pressure-path-length product than heretofore. Assignments are reported for high- K 2 ν 8 subbands in the ground state ( n=0) of the ν 12 torsion, and for 2ν 8+ν 12−ν 12 (n=1) and 2 ν 8+2 ν 12−2 ν 12 ( n=2) torsionally excited combination subbands. Upper-state υ 8=2 term values have been fitted to series expansions in powers of J( J+1) to obtain J-independent substate origins defining the torsion- K-rotation structure of the overtone state. Perturbations due to Coriolis and asymmetry resonances have been observed and characterized, as well as J-localized level-crossing resonances arising principally from interactions with the υ 7=2 overtone state of the in plane CH 3-rocking mode and the ( υ 7, υ 8)=(1,1) combination state. Differences between υ 8=2 and υ 8=1 term values have been used to generate a predicted map of the weak 2 ν 8– ν 8 CO-stretching hot band. The hot band underlies the main ν 8 fundamental in the 10-μm region, so is of significance to the determination of the fundamental line intensities. A number of the weak hot-band lines have been observed in the 10-μm FTIR spectrum.