Investigations into the millimeter and submillimeter-wave spectrum of perdeuterated methanol, CD3OD, in its ground and first excited torsional states

The rotational spectrum of CD3OD in its ground and first excited torsional states has been recorded in three frequency windows 78-119, 705-750, and 812-903 GHz in order to improve our model Hamiltonian [L.-H. Xu, H.S.P. Müller, F.F.S. van der Tak and S. Thorwirth, J. Mol. Spectrosc. 228 (2004) 220-229] that had been developed for searching for CD3OD in the interstellar medium. In the present study, 103 transitions for vt=0 and 82 transitions for vt=1 have been assigned, reaching J and K quantum numbers of 25 and 14, respectively. The observed and calculated transition frequencies in the ground and first excited torsional states agree on the average to within ∼100 and 200 kHz, respectively. Thus, the majority of the transitions, particularly those in the ground torsional state, could be reproduced within or close to their experimental uncertainties of 20-100 kHz. The reproduction of the data proved to be more challenging at higher J and K, particularly in the first excited torsional state, where the data set is more sparse than at lower quantum numbers.