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 farinfrared 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.
NHD_{2} tunnels between two equivalent positions
as does the main isotopomer NH_{3}.
The strong ctype transitions occur between the
tunneling substates whereas btype 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 spinstatistical 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 1_{01} 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 ^{14}N 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 ^{14}N 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 spinweight 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}.
