Rotational spectroscopy and bound state calculations of deuterated NH3-H2 van der Waals complexes

Pure rotational transitions of the deuterated NH3-H-2 weakly bound complexes formed by NH3/ND3 and H-2/D-2, namely ND3-H-2, NH3-D-2 and ND3-D-2, have been detected. Three different techniques, a millimeter-wave intracavity jet OROTRON spectrometer, molecular beam Fourier transform microwave (FTMW) cavity spectrometer and the broadband chirped pulse (CP) FTMW spectrometer were used to record the spectra in the frequency range from 20 to 140 GHz. The double resonance method was additionally applied to extend the frequency range of the OROTRON spectrometer to lower and of the FTMW cavity spectrometer to higher frequencies. A search for the transitions of deuterated isotopologues and their assignments were based on the recent study of the main isotopic species NH3-H-2 [L.A. Surin et al., Astrophys. J., 838, 27 (2017)] and further confirmed by the bound state calculations presented here. The measured line positions including hyperfine splitting due to the N-14 nuclear spin of NH3/ND3 and the D nuclear spins of D-2 were analysed in order to determine the molecular parameters and structure of the deuterated NH3-H-2 complexes. This study provides an effective new probe of the intermolecular interaction between ammonia and dihydrogen, knowledge of which is important for numerical modelling of astrophysical environments. (C) 2021 Elsevier Inc. All rights reserved.