The NH and ND stretching fundamentals of 14NH2D

High resolution (0.004 cm−1 instrumental bandwidth) interferometric Fourier transform infrared spectra of mixtures of ammonia-HD isotopomers were measured on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. We report the analysis of the ND and NH stretching fundamentals of 14NH2D with term values Tv (s) = 2506.5087(9) cm−1 and Tv (a) = 2505.8952(10) cm−1 for the ν1 fundamental, Tv (s) = 3365.2435(9) cm−1 and Tv (a) = 3367.5892(10) cm−1 for the ν3a fundamental and Tv (s) = 3438.8633(12) cm−1 and Tv (a) = 3439.0315(14) cm−1 for the ν3b fundamental. This notation for the fundamentals is chosen for simplicity and for analogy with the case of NH3 and ND3. The degenerate modes of NH3 and ND3, whose degeneracy is lifted in NH2D are distinguished by the subscripts a and b, being symmetric, respectively antisymmetric with respect to the ND-plane of symmetry. About 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. Assignments were established with certainty by means of ground state combination differences. The results are important for and are discussed in relation to the mode selective inhibition of inversion at the nitrogen atom by exciting ND and NH stretching vibrations, for treatments of isotope effects on inversion of ammonia through effective hamiltonians as well as true molecular hamiltonians on high dimensional potential hypersurfaces.