Microwave and radiofrequency spectra of the Arsdot;SO2van der Waals molecule have been studied by molecular beam spectroscopy. The molecule hasCspoint group symmetry and tunnels through a very low barrier at aC2vstructure at a 980 MHz rate. The tunneling interchanges the two oxygen atoms which causes half of each inversion doublet to have zero statistical weight. The inversion frequency and assumptions about the bending vibration lead to a barrier height of quest;10 cmminus;1. Stark effect measurements give mgr;a=0.2674 D, mgr;b=0.0 D, mgr;c=1.465 D. These moments are interpreted in terms of a vibrational amplitude of 24deg; associated with the inversion coordinate. The geometry of the complex is essentially perpendicular with the Ar atom above the plane of SO2and located almost directly over the SO2centerhyphen;ofhyphen;mass at a 3.675 Aring; distance.
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