Rotational Spectra of the
Ar–Ar–NH3 and Ne–Ne–NH3 van der Waals Trimers.
Jennifer van Wijngaarden and Wolfgang Jäger
Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2, Canada
Rotational spectra of Ar–Ar–NH3 and Ne–Ne–NH3 were measured between 4 and 23 GHz using a pulsed jet Fourier transform microwave spectrometer. Isotopomers containing 14NH3 and 15NH3 were studied in combination with Ar–Ar, 20Ne–20Ne, 22Ne–20Ne and 22Ne–22Ne. For the Ar–Ar–NH3 complex, the b-axis is the symmetry axis and only b-type transitions were observed. In contrast, the 20Ne–20Ne and 22Ne–22Ne isotopomers have dipole moments along their a-axes and as a result, only a-type transitions were measured. The reduced symmetry of 22Ne–20Ne–NH3 allowed the observation of both a- and b-type transitions. The spectra were fitted using an asymmetric rotor model and the resulting rotational constants were used to estimate the effective structures. Nuclear quadrupole hyperfine structure arising from the 14N nucleus was resolved. The corresponding quadrupole coupling costants were determined and analyzed in terms of the intermolecular dynamics.