Global Fit of Torsional-Rotational Transitions in the Ground and First Excited Torsional States of Methanol

✍ Scribed by L.H. Xu; J.T. Hougen

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 640 KB
• Volume: 173
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1995.1255

✦ Synopsis

Methanol data for (v_{\mathrm{t}}=0) (below the barrier) and (v_{\mathrm{t}}=1) (straddling the barrier) have been treated, using a program based on the formalism of Herbst et al. (J. Mol. Spectrosc. 108, 42-57, 1984). Altogether, 909 microwave lines (mostly assigned a (50 \mathrm{kHz}) measurement uncertainty) and 197 tunable far-infrared lines (mostly assigned 100 or (200 \mathrm{kHz}) uncertainties) in the range (K \leqslant 12, J \leqslant 20) and 5549 Fourier-transform far-infrared lines (assigned an uncertainty of 0.0002 (\mathrm{cm}^{-1}=6 \mathrm{MHz}) ) in the range (K \leqslant 14, J \leqslant 20) have been globally fit to give a unitless weighted standard deviation of 1.032 , using 56 adjustable and 8 fixed parameters. Some difficulties remain in fitting high (K) and (J b)-type tunable far-infrared lines. Although these difficulties may arise from deficiencies in the model, it also seems possible that some measurement problems still remain in the tunable far-infrared data set. Apart from the high (K) and (J) difficulties with this latter data set, a very satisfactory fit has been achieved, leading us to the conclusion that up through the first excited torsional level, a traditional one-dimensional internal rotation model is capable of accurately describing methanol energy levels, without consideration of other large-amplitude-motion effects, such as those arising, for example, when the (\mathrm{OH}) bending vibration carries the molecule to a (C_{3 \mathrm{v}}) configuration and the internal rotation barrier vanishes. 1995 Academic Press, Inc.