Analysis of torsion-rotational transitions in the first three torsional states of CH3OD

In the framework of systematic analysis and fitting of transition frequenci es of methanol isotopomers with a reduced torsion-rotational Hamiltonian th at is obtained from the one-large-amplitude internal rotation model, 1126 F ourier transform far-infrared (FIR) transitions involving the second excite d torsional level (nu(t) = 2) have been added to the data set of Duan and M cCoy [J. Mel. Spectros. 199 (2000) 302] to achieve a global fit of the obse rved high resolution microwave (MW), millimeter wave (MMW) and Fourier tran sform FIR spectra for CH3OD. The CH3OD data set contains 460 MW and MMW tra nsitions and 3474 Fourier transform FIR transitions with nu(t) less than or equal to 2 and J less than or equal to 21. The MW and MMW transitions have been fit with a root-mean-square (rms) deviation of 0.12 MHz, whereas FIR transitions have a rms deviation of 0.00026 cm(-1). These deviations are ap proximately equal to the experimental uncertainties, indicating that the MW , MMW and FIR spectral transitions have been fit to an accuracy approaching the experimental uncertainties and the reduced torsion-rotational Hamilton ian model is capable of accurately describing CH3OD energy levels up throug h the second excited torsional level. The success of the fit demonstrates t hat the increased general asymmetry in CH3OD can be taken care adequately b y the reduced Hamiltonian model. (C) 2000 Elsevier Science B.V. All rights reserved.