The observed transitions were summarized in
(1) C. P. Endres, H. S. P. Müller, S. Brünken, D. G. Paveliev, T. F. Giesen, S. Schlemmer, and F. Lewen, 2006, J. Mol. Struct. 795, 242.
Besides from (1), the data set includes transition frequencies measured with microwave accuracy from
(2) M. T. Weiss and M. W. P. Strandberg, 1951, Phys. Rev. 83, 567;
(3) M. Lichtenstein, J. J. Gallagher, and V. E. Derr, 1964, J. Mol. Spectrosc. 12, 87;
(4) F. C. de Lucia and P. Helminger, 1976, J. Mol. Spectrosc. 54, 200;
(5) E. A. Cohen and H. M. Pickett, 1982, J. Mol. Spectrosc. 93, 83;
and from
(6) L. Fusina, D. di Lonardo, J. W. C. Johns, and L. Halonen, 1988, J. Mol. Spectrosc. 127, 240.
Moreover, extensive far-infrared data were taken from (6). See (1) for detail on the uncertainties assigned to the FIR data. Some transitions with large residuals were omitted from the final fit. Transitions with uncertainties larger than 100 kHz were not merged.
With respect to version 2 from Jan. 2007, the experimental uncertainties from (2), (3), and (5) were corrected. This leads to minute changes in the predictions.
Transitions up to J = 15 and K_a = 9 should be found fairly close to the predictions. This should not be a a limitation for astronomical observations.
NHD₂ tunnels between two equivalent positions as does the main isotopomer NH₃. The strong c-type transitions occur between the tunneling substates whereas b-type transitions occur within the states. The antisymmetric, J = 0 state, in the catalog with the state number 1, is higher than the symmetric, J = 0 state by 0.1707 cm^–1 or 5118.9 MHz. The rotational constants are average values.
In addition, one has to distinguish between ortho and para levels with a spin-statistical weight ratio of 2 : 1. In the symmetric substate, the ortho and para levels are described by K_a + K_c even and odd, respectively, while it is reversed for the antisymmetric substate. The 1₀₁ level is the lowest para and ortho level within the symmetric and antisymmetric substate, respectively. It is 9.0971 and 9.2677 cm^–1 above the symmetric J = 0 level, respectively. Note, however: The ortho/para energy difference is only 0.1707 cm^–1 because of the different symmetries of v = 0 and 1 ! Since ¹⁴N hyperfine splitting may be resolved for low values of J, a separate calculation is provided for J up to 5 and up to 2 THz. The partition function takes into account the spin multiplicity g_I = 3 of the ¹⁴N nucleus !
In addition, 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. Both predictions include hyperfine splitting.
The dipole moment was derived in (1) from (5). The positive value ofthe interaction constant F_bc affords a positive value for μ_b.