LI-HONG XU, M. ABBOUTI TEMSAMANI, Department of Physical Sciences, University of New Brunswick, N.B. Canada E2L 4L5; X. WANG, Y. MA, A. CHIROKOLAVA, T. J. CRONIN AND D. S. PERRY, Department of Chemistry, University of Akron, Ohio 44325-3610.
The 3µm spectrum of methanol is an important gateway to the understanding of molecular dynamics and to the modeling of cometary spectra. The region is extremely complicated due to a dense vibrational structure and network of interactions among the three CH-stretch fundamentals, 2, 9, 3, six overtones and combinations of the three CH3-bending modes, 4, 10, 5, and a variety of overtone combinations of the torsion 12, with the remaining lower-lying vibrations.
We have obtained FT spectra for the 3µm region under various conditions. The structure is dense with few easily recognized features above the 3 symmetric CH-stretch. However, in an extension of the color-center-laser slit-jet beam spectrum from 2945 to 2975 cm-1, low K states could be identified, then allowing further assignment and confirmations of the medium K states from FTS. Altogether, about 25 vibration-torsion- K -rotational states have now been firmly assigned up to K = 4. Plots of K -reduced energies place these states into three distinguishable groups assigned as 9, 2 4, and 4+ 10, although there are a number of extra subbands in the spectrum arising possibly from interactions with other states. Spectroscopic findings at the present time are: (i) the torsional A/E ordering is inverted for 9, normal for 2 4, and apparently normal for the presently observed K = 2 states of 4+ 10; (ii) the K = 0 torsional A/E splittings are -5.48 and 8.28 cm-1 for 9 and 2 4, respectively, and an estimated much lower than ground state value for the 4+ 10 combination; (iii) the 9 and 2 4 states have virtually identical upper state term values around 3092 cm-1, but show almost equal and opposite linear shifts with K with slopes of 2-3 cm-1/ K -value; (iv) the 4+ 10 combination is about 20 cm-1 lower in energy than 9 and 2 4, 10 cm-1 lower than the previous estimates for the band center.