title: Microwave spectrum of the H2DO+ ion: inversion-rotation transitions and inversion splitting.
abstract: Inversion-rotation spectral lines of the monodeuterated hydronium ion, H(2)DO(+), have been observed by a source-modulation spectrometer in the millimeter- to submillimeter-wave region. The ion was generated by a hollow-cathode discharge in a gas mixture of H(2)O and D(2)O. Nine inversion-rotation lines were measured precisely for the lowest pair of inversion doublets in the frequency region from 210 to 720 GHz. The measured lines were analyzed to derive rotational constants in the inversion-doublet states and inversion splitting. The inversion splitting in the ground state was determined to be 1,215,866(410) MHz, that is, 40.5569(137) cm(-1), where the numbers in parentheses give probable uncertainties estimated from the Jacobian matrix of the assumed centrifugal distortion constants of the inversion-doublet states. The determined inversion splitting is off by -0.58 cm(-1) from the predicted value of 41.14 cm(-1) by Rayamaki et al. using high-order coupled cluster ab initio calculations [J. Chem. Phys. 118, 10929 (2003)], and by 0.039 cm(-1) from the observed value of 40.518(10) cm(-1) by Dong and Nesbitt using high-resolution jet-cooled infrared spectroscopy [J. Chem. Phys. 125, 144311 (2006)] beyond the quoted uncertainty. The most astronomically important transition 0(00)(-)-1(0)(+) for the ortho species was measured at 673,257.024(31) MHz, which could be used as a radioastronomical probe investigating interstellar chemistry of deuterium fractionation in space.
authors.affiliation: Research Center for Development of Far-Infrared Region, University of Fukui, Bunkyo, Fukui 910-8507, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Furuya
authors.forename: Shuji
authors.initials: S
authors.lastname: Saito
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Araki