Knowledge Bank

Recently reported progress on the analysis of Fourier transform spectra of the O-18 and C-13 isotopomers of $methanol1-3$ has illuminated the torsion-rotation energy level structure of the in-plane $CH3$-rocking and OH-bending modes. Extension of these insights to the parent $CH3OH$ isotopic species has permitted assignment of several subbands in the n = 1 torsionally excited in-plane $CH3$-rocking band of normal $CH3OH$. The subband pattern is very similar to that of the C-13 species with a relatively small upward isotopic shift. One of the subbands identified is the K = 2 subband of A torsional symmetry, which shows substantial asymmetry doubling. The splitting constants are very different in the ground and excited states, suggesting strong Fermi mixing between the $n=1CH3$-rocking state and the n = 0 OH-bending state, as found previously for the O-18 and C-13 $species.1,3$ The Fermi mixing between modes is likely a principal reason that the low-resolution methanol spectrum shows no clear band structure in the region of the OH-bend but simply a broad, rather featureless peak which has been something of an enigma for a very long time. Analysis of the high-resolution $CH3OH$ spectrum in this region is also underway, and it is hoped that keys to the gateway will shortly be found in order to shine some light on the fertile spectroscopic pastures within.