Structure, properties, and inversion of the Ar·SO₂ van der Waals molecule

Microwave and radiofrequency spectra of the Ar·SO₂ van der Waals molecule have been studied by molecular beam spectroscopy. The molecule has C_s point group symmetry and tunnels through a very low barrier at a C_2v structure 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 ≈10 cm^-1. Stark effect measurements give μ_a=0.2674 D, μ_b=0.0 D, μ_c=1.465 D. These moments are interpreted in terms of a vibrational amplitude of 24° associated with the inversion coordinate. The geometry of the complex is essentially perpendicular with the Ar atom above the plane of SO₂ and located almost directly over the SO₂ center-of-mass at a 3.675 A° distance.