15min:
THE 3µm VIBRATION-TORSION-ROTATION ENERGY MANIFOLD OF METHANOL.

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, nu2, nu9, nu3, six overtones and combinations of the three CH3-bending modes, nu4, nu10, nu5, and a variety of overtone combinations of the torsion nu12, 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 nu3 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 nu9, 2 nu4, and nu4+ nu10, 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 nu9, normal for 2 nu4, and apparently normal for the presently observed K = 2 states of nu4+ nu10; (ii) the K = 0 torsional A/E splittings are -5.48 and 8.28 cm-1 for nu9 and 2 nu4, respectively, and an estimated much lower than ground state value for the nu4+ nu10 combination; (iii) the nu9 and 2 nu4 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 nu4+ nu10 combination is about 20 cm-1 lower in energy than nu9 and 2 nu4, 10 cm-1 lower than the previous estimates for the band center.