The observed pure tunneling transitions were taken from
(1) S. G. Kukolich, 1968, Phys. Rev. 172, 59;
in part corrected in
(2) J. T. Hougen, 1972, J. Chem. Phys. 57, 4207;
and from
(3) H. Sasada, 1980, J. Mol. Spectrosc. 83, 15.
Accurate rotation-inversion transitions were reported by
(4) S. P. Belov, T. Klaus, G. M. Plummer, R. Schieder, and G. Winnewisser, 1995, Z. Naturforsch. 50a, 1187;
and from
(4) G. Winnewisser, S. P. Belov, T. Klaus, and S. Urban, 1996, Z. Naturforsch. 51a, 200.
Further transition frequencies have been obtained by FIR spectroscopy from
(5) S. Urban, S. Klee, and K. M. T. Yamada, 1994, J. Mol. Spectrosc. 168, 384;
and from
(6) M. Carlotti, A. Trombetti, B. Velino, and J. Vrbancich, 1980, J. Mol. Spectrosc. 83, 401.
The data from (6) has not been merged, that from (5) has been merged to a large extent.
¹⁵NH₃ tunnels between two equivalent positions as does the main species NH₃; the energy difference in the former is with 0.7577 cm^–1 slightly smaller than in the latter.
The rotational constants are average values. Some parameters were kept fixed to those of the main isotopologue. They were derived from the data set described in
(7) P. Chen, J. C. Pearson, H. M. Pickett, S. Matsuura, and G.A. Blake, 2006, J. Mol. Spectrosc. 236, 116.
With respect to the first entry of May 2008, several modifications were made. Ab initio calculations by
(8) X. Huang, D. W. Schwenke, and T. J. Lee, 2011, J. Chem. Phys. 134, Art. No. 044321;
(9) X. Huang and T. J. Lee, 2010, personal communications;
suggested that the C rotational constant could not be determined reliably from the present data set. Ab initio energies yielded C_{0, avg}(¹⁵NH₃) about 8 MHz larger than that of ¹⁴NH₃. The average ground state value for C – B was hence kept fixed to the value derived that way. In addition, the lowest allowed rotational level was put at an energy of zero. This has minor effects at elevated temperatures, but rather large ones at very low temperatures. Predictions of transitions with ΔK = 0 should be good to at least 4 THz and probably quite reasonable up to about 10 THz. Transitions with ΔK = 3 should be viewed with great caution.
At low temperatures, it is necessary to discern betweenA-¹⁵NH₃ and E-¹⁵NH₃. The A state levels are described by K = 3n, those of E state by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-¹⁵NH₃ with K > 0 and all other states, respectively. The J_K = 1₁ level of the lower tunneling substate (v = 0) is the lowest E state level. It is 15.3913 cm^–1 above ground. Separate E and A predictions are available along with separate E and A partition function values.
The dipole moment and its first order distortion corrections were taken from
(10) K. Tanaka, H. Ito, and T. Tanaka, 1987, J. Chem. Phys. 87, 1557.