Infrared spectroscopy of 14ND3: Analysis of the ν2/ν4/2ν2 and ν1/ν3/2ν4 band systems

Abstract The high resolution infrared spectrum of 14 ND 3 has been re-investigated in the intervals 450–1600 cm −1 and 2200–2800 cm −1 , where the absorption lines of the ν 2 /ν 4 /2ν 2 and ν 1 /ν 3 /2ν 4 band systems are located. The analysis of the bending fundamentals ν 2 and ν 4 has been extended assigning 844 transitions belonging to the 2ν 2 and 2ν 2 ←ν 2 cold and hot bands. In total, 3436 transitions, of which 3358 are vibration−rotation−inversion and 78 inversion transitions in the v 2 =1 state [Urban S et al. J Mol Spectrosc 1984;106:29-37] have been fitted simultaneously. The effective Hamiltonian adopted for the analysis includes all symmetry allowed interactions between and within the studied excited state levels. Accurate values of the spectroscopic parameters for both inversion components of the v 2 =1, 2 and v 4 =1 states have been obtained. The inversion transitions are reproduced at 1.8 times their experimental estimated precision, while the infrared data are reproduced at 1.5 times their uncertainties. The assignments of the stretching fundamentals ν 1 and ν 3 have been extended to higher J and K transitions. The number of transitions of ν 1 has been doubled and it has been increased by 23% for ν 3 . In addition, 805 transitions reaching the v 4 =2 0 and 2 ±2 s , a states have been identified. In total, 2408 transitions of the ν 1 /ν 3 /2ν 4 band system have been fitted simultaneously. The adopted effective Hamiltonian includes also the Fermi resonance terms between v 1 =1 and v 4 =2 0 and higher order Coriolis terms between v 1 =1/v 4 =2 ±2 , v 3 =1/v 4 =2 0 , and v 3 =1/v 4 =2 ±2 . The model adopted to rationalize the entangled network of energy levels has been moderately successful. The standard deviation of the fit, 0.0090 cm −1 , is 9 times the estimated measurement precision. Finally, an improved set of ground state parameters has been derived.