Microwave spectra of the Ar-ND_3 van der Waals complex and its partially protonated isotopomers

摘要

Rotational spectra of the Ar—ND3 van der Waals complex were measured in the frequency range between 4 and 19 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The isotopomers studied include those with ND3, NHD2, and NH2D. A tunneling splitting due to the inversion of the ammonia subunit within the ground state of the complex was observed for all three isotopomers. This splitting cannot be measured in Ar—NH3 for spin statistical reasons. Nuclear quadrupole hyperfine structure of rotational transitions arising from the ‘4N nucleus was resolved and the corresponding nuclear quadrupole coupling constants were determined. A smaller nuclear quadrupole splitting arising from the deuterium nuclei was observed but not resolved. The ground state spectroscopic constants are compared with experimental and theoretical data previously reported for Ar—NH3. Additional transitions were observed for Ar—ND3 and assigned to the two inversion tunnelling states of an excited internal rotor state. A fit of the spectroscopic constants for these two states suggests the presence of a Coriolis perturbation along the lines of that observed in the microwave spectrum of Ar—NH_3.