The rotational spectra of HD17O and D2(17)O: experiment and quantum-chemical calculations.

Guided by theoretical predictions, the rotational spectrum of HD(17)O was recorded and assigned for the first time, while the measurements for D(2)(17)O were extended up to the THz region. For both isotopic species, a large portion of the rotational spectrum, from 65 GHz (from 200 GHz for the bideuterated isotopologue) up to 1.6 THz, was investigated, thus allowing the accurate determination of the ground-state rotational and centrifugal-distortion constants. Considering that the rotational spectra of water isotopologues are characterized by a very low density of lines and strong centrifugal-distortion effects, the accurate quantum-chemical prediction of the relevant spectroscopic parameters played a crucial role in the line search and assignment as well as in supporting the fitting procedure. In addition to rotational and centrifugal-distortion constants, the knowledge of the oxygen quadrupole-coupling constants was essential, as the corresponding interaction leads to characteristic features (hyperfine structure) that enabled proper line assignments.