The observed transitions were published in
(1) M. Elkeurti, L. H. Coudert, J. Orphal, G. Wlodarczak, C. E. Fellows, S. Toumi, 2008, J. Mol. Spectrosc. 251, 90.
The spectroscopic parameters of NHD₂ were used as starting values in the present fits. Based on the fit results it was concluded that some weak transitions from (1) may have been assigned incorrectly. The resulting parameters are consequently different from those in (1). Nevertheless, predictions for low energy transitions are beyond any doubt. Moreover, predictions with calculated uncertainties below 1 MHz should be reliable because of the extensive far-infrared data which have not been merged.
The misassignments have recently been confirmed in
(2) M. Elkeurti, L. H. Coudert, J. Orphal, G. Wlodarczak, C. E. Fellows, S. Toumi, 2010, J. Mol. Spectrosc. 260, 139.
¹⁵NHD₂ tunnels between two equivalent positionsas does the main species 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 0.1583 cm^–1 or 4746.5 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 9.0813 and 9.2395 cm^–1 above the symmetric J = 0 level, respectively. Note, however: The ortho/para energy difference is only 0.1583 cm^–1 because of the different symmetries of v = 0 and 1 ! The dipole moment was assumed to agree with that of ¹⁴NHD₂; see e019501.cat.