Fourier transform spectra and torsion–rotation structure of the CO-stretching 2n8 overtone and 2n8 –n8 hot band of CH3OH

The Fourier transform infrared (FTIR) spectrum of the 2n8 overtone band of the CO-stretching vibrational mode of CH3OH has been investigated in the 5-mm region at a spectral resolution of 0.0048 cm21 (1/MOPD) and a higher pressure-path-length product than heretofore. Assignments are reported for high-K 2n8 subbands in the ground state ðn ¼ 0Þ of the n12 torsion, and for 2n8 þn12 2n12 ðn ¼ 1Þ and 2n8 þ 2n12 2 2n12 ðn ¼ 2Þ torsionally excited combination subbands. Upper-state y 8 ¼ 2 term values have been fitted to series expansions in powers of JðJ þ 1Þ 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 y 7 ¼ 2 overtone state of the in plane CH3-rocking mode and the ðy 7; y 8Þ ¼ ð1; 1Þ combination state. Differences between y 8 ¼ 2 and y 8 ¼ 1 term values have been used to generate a predicted map of the weak 2n8 –n8 CO-stretching hot band. The hot band underlies the main n8 fundamental in the 10-mm 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-mm FTIR spectrum. q 2003 Elsevier B.V. All rights reserved