Microwave Rotational Spectra of the
Ar–C2H4 and Ne–C2H4 van der Waals Dimers.
Yaqian Liu and Wolfgang Jäger
Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2, Canada
Rotational spectra of various isotopomers of the Ar–C2H4 and Ne–C2H4 van der Waals dimers were measured in the frequency range from 3.5 to 22 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The observed transitions are all of a-type. The observed spectra are consistent with planar, T-shaped equilibrium geometries. Tunneling splittings were observed for all transitions. This is attributed to an internal rotation motion of the ethylene unit within the complex. Ne–C2H4 shows a larger tunneling splitting than Ar–C2H4, which can be attributed to a lower tunneling barrier in the Ne–C2H4 case. Molecular symmetry group analyses using nuclear permutation inversion group theory can explain the observed intensity variation and the absence of certain transitions. Effective separations between the center-of-mass of ethylene and the rare gas atoms were obtained from the ground state rotational constants. ab initio calculations at the MP4 level were carried out on Ne–C2H4, and the results were compared with those from the experiments.