Microwave Spectra of the Ar3–NH3 and Ne3–NH3 van der Waals Tetramers.
Jennifer van Wijngaarden and Wolfgang Jäger
Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2, Canada
Rotational spectra of the Ar3–NH3 and Ne3–NH3 van der Waals complexes were measured between 4 and 18 GHz using a pulsed jet Fourier transform microwave spectrometer. The isotopomers studied include those of NH3, 15NH3, ND3, ND2H, and NDH2 in combination with Ar3, 20Ne3, 22Ne3, 20Ne222Ne, and 20Ne22Ne2. The isotopomers containing Ar3, 20Ne3, and 22Ne3 are symmetric tops for which a-type transitions with K = 3n (n = 0, 1, 2, ...) were observed. The other isotopomers are asymmetric tops and due to the reduced symmetry, all rotational levels are present in these complexes. For 20Ne222Ne, both a- and b-type transitions were observed whereas the slightly different mass distribution in 20Ne222Ne led to the detection of a- and c-type transitions. For the deuterium containing isotopomers, each rotational transition is split by the inversion motion of ammonia within the complex. This inverison splitting is not observed in the NH3 and 15NH3 containing species for spin statistical reasons. The spectroscopic constants, including the 14N nuclear quadrupole coupling constants, were fit for each isotopomer and used to derive structural and dynamical information for the Ar3–NH3 and Ne3–NH3 van der Waals complexes.