15min:

JENNIFER VAN WIJNGAARDEN AND WOLFGANG JÄGER, Department of Chemistry, University of Alberta, Edmonton, AB, Canada, T6G 2G2.

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 ^20 Ne₂²²Ne, both a- and b-type transitions were observed whereas the slightly different mass distribution in ^20 Ne₂²²Ne 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 ^15 NH₃ 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.