The observed transitions were taken from
(1) F. C. de Lucia and P. Helminger, 1976, J. Mol. Spectrosc. 54, 200;
(2) E. A. Cohen and H. M. Pickett, 1982, J. Mol. Spectrosc. 93, 83;
and from
(3) L. Fusina, D. di Lonardo, J. W. C. Johns, and L. Halonen, 1988, J. Mol. Spectrosc. 127, 240.
Using three additional higher order centrifugal distortion parameters compared to the ones from (3), it was possible to fit the transition frequencies within experimental uncertainties on the average.
NH₂D tunnels between two equivalent positions as does the main isotopomer NH₃. The strong c-type transitions occur between the tunneling substates whereas a-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 0.4059 cm^–1 or 12169.4 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 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 14.3725 and 14.7761 cm^–1 above the symmetric J = 0 level, respectively.
Since ¹⁴N hyperfine splitting may be resolved for low values of J, a separate calculation is provided for J up to 10. The partition function takes into account the spin multiplicity g_I = 3 of the ¹⁴N nucleus !
July 2017: separate para and ortho predictions with hyperfine splitting are available up to J = 4 and 2600 GHz along with separate para and ortho partition function values. The dipole moment was taken from (2). The negative value of the interaction constant F_ac affords a negative value for μ_a.