Global Fit of Torsion–Rotation Transitions in the Ground and First Excited Torsional States of13C-Methanol

✍ Scribed by Li-Hong Xu; M.S. Walsh; R.M. Lees

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 551 KB
• Volume: 179
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.0206

✦ Synopsis

A global treatment of reported microwave, millimeter-wave, and Fourier-transform far-infrared (FIR) spectra of the C-13 isotopic species of methanol has been carried out for the first two torsional states ( n t Å 0 below the barrier and n t Å 1 straddling the barrier) of the ground vibrational state. The 13 CH 3 OH data set contains 725 microwave and millimeter-wave lines and 6283 Fourier-transform far-infrared lines, representing the most recent available information in the quantum number ranges J £ 20, K £ 14. The transitions have been successfully fitted to within the assigned measurement uncertainties of {50 kHz for most of the microwave and millimeter lines and {6 MHz for the FIR lines with the use of a program (I. Kleiner and M. Godefroid, private communication) based on the formalism of Herbst et al. (J. Mol. Spectrosc. 108, 42-57 (1984)). A convergent global fit was achieved using 55 adjustable and 2 fixed parameters to reach an overall weighted standard deviation of 0.962, giving further confirmation that a traditional onedimensional internal rotation model can accurately describe methanol energy levels up through the first excited torsional state. Our new parameters for C-13 methanol are compared to previous global fitting results for the normal 12 CH 3 OH isotopomer. Calculations employing these parameters reveal possible C-13 assignments for 28 lines appearing in natural abundance in a newly measured methanol microwave atlas from 7 to 200 GHz compiled by the group at Toyama University in Japan.