High resolution spectroscopy in the second excited torsional state of CH 3OD and the atlas of the Fourier transform spectrum in the range 20–205 cm −1

Abstract

In this work, the reduced eighth order Hamiltonian that has been used for the determination of the molecular parameters—using the high resolution Fourier transform far-infrared (FIR) assigned transitions in the ground and first excited torsional states of CH 3OD—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 global fit including all the assigned transitions up to the second excited state. Additionally, in this paper we present the detailed Fourier transform spectral map of CH 3OD in the range 20–205 cm −1, as was done for the parent species. This spectral map will be very valuable for radio astronomers looking for D/ H ratios in the interstellar space.