The first entry of May 2012 was reevaluated. Details are given in
(1) S. Muller, H. S. P. Müller, J. H. Black, et al., 2016, Astron. Astrophys. 595, Art. No. A128.
The main differences are a slightly modified set of spectroscopic parameters, rest frequencies for the 1_1,0 – 1_0,1 transition near 620 GHz from astronomical observations with ALMA. In addition, the entire HFS pattern of stronger fine structure component of the 1_1,1 – 0_0,0 transition near 1115 GHz was shifted 5 MHz up in frequency, whereas the weaker component near 1140 GHz was shifted 5 MHz down. The first shift was suggested in
(2) D. A. Neufeld, J. R. Goicoechea, P. Sonnentrucker, et al., 2010, Astron. Astrophys. 521, Art. No. L10,
whereas the second shift is an estimate from trial fits. There are still no laboratory data available for oxidaniumyl with microwave accuracy. However, there have been two studies employing laser magnetic resonance (LMR) with uncertainties of order of 1 MHz. Usually, transition frequencies extrapolated to zero field are not published. One of the two articles provide such frequencies, albeit only for the data obtained in the course of their investigation. The zero field frequencies appear to be reliable within the stated uncertainties. Weighted averages were derived wherever applicable. The data were taken from
(3) P. Mürtz, L. R. Zink, K. M. Evenson, and J. M. Brown, 1998, J. Chem. Phys. 109, 9744.
In that work, additional LMR data were taken from
(4) S. E. Strahan, R. P. Mueller, and R. J. Saykally, 1986, J. Chem. Phys. 85, 1252.
Only the calculated (sic !) frequencies for the 1₁₁ – 0₀₀ transition were published in (1). These frequencies were used in the current analysis with uncertainties of 0.00006 cm^–1.
Rovibrational data from observations of fundamental transitions were also used in the fit. These were reported by
(5) B. M. Dinelli, M. W. Crofton, and T. Oka, 1988, J. Mol. Spectrosc. 127, 1;
by
(6) P. R. Brown, P. B. Davies, and R. J. Stickland, 1989, J. Chem. Phys. 91, 3384.
by
(7) T. R. Huet, C. J. Pursell, W. C. Ho, B. M. Dinelli, and T. Oka, 1992, J. Chem. Phys. 97, 5977;
and by
(8) R. Zheng, S. Li, S.-Y. Hou, G.-M. Huang, and C.-X. Duan, 2008, Chin. Phys. B 17, 4485.
Furthermore, ground state combination differences (GSCDs) were included. These were reported by
(9) H. Lew, 1976, Can. J. Phys. 54, 2028;
and by
(10) T. R. Huet, I. Hadj Bachir, J.-L. Destombes, and M. Vervloet, 1997, J. Chem. Phys. 107, 5645.
The data from (9) were kindly provided in electronic form by B. M. Dinelli via P. Mürtz.
Some predicted uncertainties exceed 1 GHz; they show up as 999.9999 in megahertz unit and as 0.03336 in inverse centimeter unit.
It is possible, though not certain, that the predictions are sufficient for astronomical purposes. Nevertheless, all predictions should be viewed with at least some caution mainly because of the slowly converging Hamiltonian, but also because of some uncertainty about the extrapolation of the LMR data to zero field. Considerable caution is advised for transitions having predicted uncertainties larger than 10 MHz.
At low temperatures, it may be necessary to discern betweenortho-H₂O⁺ and para-H₂O⁺. The ortho states are described by K_a + K_c even, the para states by K_a + K_c odd. There are three times as many levels for ortho-H₂O⁺ than there are for para-H₂O⁺. Thus, for transitions with unresolved ¹H hyperfine splitting the nuclear spin-weight ratio is 3 : 1 between ortho-H₂O⁺ and para-H₂O⁺. However, for transitions with resolved ¹H hyperfine splitting no non-trivial spin-statistics have to be considered. The N_KaKc = 1₀₁, J + 1/2 = 2 is the lowest para state, It is 20.8582 cm^–1 above ground. Separate para and ortho predictions are available along with separate para and ortho partition function values. These entries have been truncated slightly more than the regular entry. Even though matrix elements exist which mix ortho and para states, frequency shifts and spin-exchange is probably negligible.
A ground state dipole moment value was calculated ab initio by
(11) B. Weis, S. Carter, P. Rosmus, H.-J. Werner, and P. J. Knowles, 1989, J. Chem. Phys. 91, 2818.