Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1)

The high resolution Fourier transform far-infrared (FIR) spectrum of the to rsion rotation band of CH,OD has been analyzed for the highly excited torsi on states (n greater than or equal to 2) in the vibrational ground state. T he spectrum shows splitting of the lines due to strong torsional-rotational -vibrational interactions in the molecule. Assignments were possible for ro tational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to similar to 30 in most cases, for all the sym metry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy exp ansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters we re able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coeff icients should prove valuable in the calculation of precise energy values f or excited torsional states up to n = 4, which is way above the torsional b arrier. The detailed high-resolution spectral atlas of CH,OD has been prese nted in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the jo urnal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer spa ce. (C) 2000 Elsevier Science B.V. All rights reserved.