Chloronium, also known as protonated HCl, is isoelectronic to H₂S. The experimental lines are from
(1) M. Araki, T. Furuya, and S. Saito, 2001, J. Mol. Spectrosc. 210, 132.
The uncertainties are assumed values and should be viewed with some caution. Overlapping lines have not been merged.
Also used in the fit were infrared transitions from
(2) K. Kawaguchi and E. Hirota, 1986, J. Chem. Phys. 85, 6910;
and from
(3) S. K. Lee, T. Amano, K. Kawaguchi, and M. Oldani, 1988, J. Mol. Spectrosc. 130, 1.
With respect to the Nov. 2009 entry, two very weak HFS components have been added for the transition 2_1,2 – 1_0,1 near 782 GHz. The version number has been retained. Thus far, only ground state transitions have been observed. Therefore, predictions should be sufficient for all astronomical purposes. More generally, predictions with uncertainties much larger than 1 MHz should be viewed with caution.
The dipole moment is from an ab initio calculation by
(4) H. S. P. Müller; 2008, unpublished.
At low temperatures, it may be necessary to discern between ortho-H₂Cl⁺ and para-H₂Cl⁺. The ortho and para states are described by K_a + K_c being odd and even, respectively. The nuclear spin-weights are 3 and 1 for ortho-H₂Cl⁺ and para-H₂Cl⁺, respectively. The J_KaKc = 1₀₁, F = 1.5 is the lowest ortho state. It is 14.0630 cm^–1 above ground.
May 2010: separate para and ortho predictions are available up to about 100 cm^–1 along with separate para and ortho partition function values. Note: the spin-weight of 3 for the separate ortho predictions has been eliminated.