Microwave rotational spectra of the Kr-NH3 van der Waals complex

Abstract

Rotational spectra of the Kr-NH3 van der Waals complex were measured in the frequency range between 4 and 24 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The isotopomers studied included those of NH3, 15NH3, ND3, NHD2, and NH2D with the five most abundant isotopes of Kr. Tunnelling splittings due to the inversion of the ammonia subunit within the ground state of the complex were observed for all three deuterium containing isotopomers. In the NH3 and 15NH3 isotopomers, one of the tunnelling states has a spin statistical weight of zero and the splitting can therefore not be measured in these species. Nuclear quadrupole hyperfine structure arising from the 14N and 83Kr nuclei was measured and the corresponding nuclear quadrupole coupling constants were determined. These were used to estimate structural parameters and derive information about the intermolecular dynamics. Smaller nuclear quadrupole splittings arising from the deuterium nuclei were observed but could not be resolved. The ground state spectroscopic constants were compared with experimental and theoretical data previously reported for Ar-NH3 and its isotopomers. For the Kr-ND3 isotopomers, additional transitions were observed and assigned to the two inversion components of an excited internal rotor state. A fit of the spectroscopic constants revealed the presence of a Coriolis perturbation, similar to that reported for this state in Ar-ND3 and Ar-NH3.