High resolution spectroscopic analysis of the v2 = 1 and v4a = 1 states of 14ND2H

• Di-deuterated ammonia. • high resolution infrared spectra. • v 2 = 1, v 4a =1. • Watson-type Hamiltonian. Transitions of ND 2 H have been detected in the high-resolution spectra of 14 ND 3 recorded in the region 60 − 1515 cm −1 , using the Bruker IFS 125 Fourier transform spectrometer located at the synchrotron far-infrared beamline, Canadian Light Source. In this study we report on the observation and analysis of transitions to and between the s, a inversion levels of the v 2 = 1 and v 4a = 1 states for ND 2 H. We assigned to v 2 = 1 (v 4 a = 1) 996 (296) rotation-inversion transitions, with J up to 19 (13), and 3578 (1966) vibration-rotation-inversion transitions from the ground state, with J ′ up to 22 (13). The newly assigned transitions, together with those present in the literature, were fitted on the basis of a Watson-type S reduced Hamiltonian using the III l representation. The model includes terms up to the 10th power of the angular momentum and vibration-rotation interaction terms between the inversion levels. Precise and extended sets of spectroscopic parameters and term values were derived for the s, a v 2 = 1 and v 4 a = 1 states as results of least squares weighted fit procedures that reproduce the transition wavenumbers at experimental accuracy.