High resolution spectroscopy in the second excited torsional state of CH3OD and the atlas of the Fourier transform spectrum in the range 20-205 cm(-1)

In this work, the reduced eighth order Hamiltonian that has been used for t he determination of the molecular parameters-using the high resolution Four ier transform far-infrared (FIR) assigned transitions in the ground and fir st excited torsional states of CH3OD-has been applied to assign and refine the model for the second excited torsional state. The data set consisted of 1220 FIR transitions with the rotational angular momentum J < 21 and K < 7 in the second excited torsional state. It should be noted that the second excited torsional states of methanol are almost at the top of the torsional barrier. Thus it was interesting to see how the large amplitude motion is taken care of by the eighth order Hamiltonian. We are in the process of a g lobal fit including all the assigned transitions up to the second excited s tate. Additionally, in this paper we present the detailed Fourier transform spectral map of CH,OD in the range 20-205 cm(-1), as was done for the pare nt species. This spectral map will be very valuable for radio astronomers l ooking for D/H ratios in the interstellar space. (C) 1999 Elsevier Science B.V. All rights reserved.