Knowledge Bank

The radiofrequency and microwave spectrum of $(SO2)2$ has been measured using the molecular beam electric resonance technique. The spectrum is characteristic of an asymmetric top in which the two nonequivalent $SO2$ subunits interchange roles through a low frequency (70 kHz) tunnelling motion. The spectroscopic constants obtained for $SO2$ dimer are: The average distance between the center of masses of the two subunits, $Rc\mu$, is 3.825(10) A. The magnitude of the weak bond stretching force constant, $kz$, is 0.0264(4) mdynes/AA The relative orientation of the subunits is not well determined, but is demonstrated to be unlike the orientation of the nearest neighbors in the sulfur dioxide crystal. Furthermore, $RCM$ differs greatly from the nearest neighbor $RCM$ observed in the crystal (4.28{\AA}).