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 torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry 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 expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented 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 journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.

Variable-temperature 3-m absorption cell developed for spectroscopic measurements of gases.

A variable-temperature absorption cell 3 m in length, which was designed and built for spectroscopic measurements of gases in combination with a Bruker IPS 120 HR interferometer, is described. The cell is surrounded by a cooling system and a heating system. The heating system consists of a computer-controlled set of 16 independent heating elements distributed over the length of the cell. The entire assembly enables measurements to be made in the temperature range from 123 to 423 K. The temperature of the cell can be stabilized within ±0.5 K over the entire length in this temperature range. The performance of the cell is discussed in relation to a spectroscopic temperature determination by the use of CO(2) intensity measurements.