The H₂DO⁺ cation undergoes large amplitude tunneling, just as the isoelectronic monodeuterated ammonia, NH₂D molecule. However, the barrier to planarity is much lower such that the two tunneling substates in the ground vibrational state are 1.216 THz apart instead of only 12.17 GHz. The strong c-type transitions occur between the tunneling substates whereas a-type transitions occur within the states. The present analysis has been described by
(1) H. S. P. Müller, F. Dong, D. J. Nesbitt, T. Furuya, and S. Saito, 2010, Phys. Chem. Chem. Phys., 12, 8362.
The antisymmetric, J = 0 state, in the catalog with the state number 1, is higher than the symmetric, J = 0 state by 40.55 cm^–1 or 1.216 THz. The rotational constants are average values.
Note: predictions have been truncated at J = 6. All predictions should be viewed with caution. Predictions with uncertainties less than 50 MHz may be fairly reliable. In addition, one has to distinguish between ortho and para levels with a spin-statistical weight ratio of 3 : 1. In the symmetric substate, the ortho and para levels are described by K_a odd and even, respectively, while it is reversed for the antisymmetric substate. The 1₁₁ level is the lowest ortho and para level in the symmetric and antisymmetric substate, respectively. It is 15.725 and 56.14 cm^–1 above the symmetric J = 0 level, respectively.
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 previous entry from Jan. 2008 was based on the following data: Rotation-tunneling transitions have been reported by
(2) T. Furuya, S. Saito, and M. Araki, 2007, J. Chem. Phys., 127, Art.-No. 244314.
Ground state combination differences were also used in the fit. They were taken from
(3) F. Dong and D. J. Nesbitt, 2006, J. Chem. Phys., 126, Art.-No. 144311.
The dipole moment was assumed to agree with that of the main species, see e019503.cat. The magnitude of the a-component was estimated in (2).
Note: IUPAC recommends to use oxidanium for H₃O⁺. This is derived from oxidane for H₂O, which is also known as water. IUPAC discourages the commonly used name hydronium.