CH2D+
Methylium, monodeuterated isotopolog
Species tag 016503
Version4*
Date of EntrySep. 2014
ContributorH. S. P. Müller

CH3+ and CD3+ do not posess a permanent dipole moment because they are planar symmetric top rotors. In contrast, both CH2D+ and CHD2+ do have a sizable dipole moment because the charge is not located in the center of mass.
With respect to the third entry from October 2013, the available data have been reconsidered and refit.
20 low-lying rotational transitions have been measured by
(1) M. Töpfer, P. Jusko, S. Schlemmer, O. Asvany, 2016, Astron. Astrophys. 593, L11.
Additional infrared data had only a small impact on the parameter values and uncertainties and were omitted. Resorting to the S reduced Hamiltonian requires one less parameter.
Predictions should be sufficiently accurate for all astronomical observations. Care is advised for transitions with calculated uncertainties larger than 0.15 MHz.
An estimate for the dipole moment was reported in
(2) M. F. Jagod, M. Rösslein, C. M. Gabrys, and T. Oka, 1992 J. Mol. Spectrosc. 153, 666.
At low temperatures, it may be necessary to discern between ortho-CH2D+ and para-CH2D+. The ortho states are described by Ka odd, the para states by Ka even. The nuclear spin-weights are 3 and 1 for ortho-CH2D+ and para-CH2D+, respectively. The JKaKc = 111 is the lowest ortho state. It is 12.89 cm–1 above ground.
Separate para and ortho predictions are available up to J = 4 along with separate para and ortho partition function values. Note: the spin-weight of 3 for the separate ortho predictions has been eliminated.
The earlier versions can also be accessed in the Cologne Spectroscopy Data section.

Lines Listed379
Frequency / GHz< 6049
Max. J21
log STR0-6.7
log STR1-5.7
Isotope Corr.-3.813
Egy / cm–10.0
 µa / D0.329
 µb / D 
 µc / D 
 A / MHz280869.8
 B / MHz172992.7
 C / MHz105707.8
 Q(300.0)780.7939
 Q(225.0)507.5502
 Q(150.0)277.0238
 Q(75.00)98.9614
 Q(37.50)35.7483
 Q(18.75)12.8013
 Q(9.375)4.1693
 Q(5.000)1.5483
 Q(2.725)1.0352
detected in ISM/CSMpossibly


Database maintained by Holger S. P. Müller and Sven Thorwirth, programming by D. Roth and F. Schloeder