Knowledge Bank

The geometrical structure of the benzene dimer has been elusive in spite of extensive $studies.1$ We report resolution of its rotational spectrum at low J(2 to 7) with a Balle/Flygare Fourier transform microwave spectrometer using a pulsed supersonic nozzle as the source. Transitions have been found which are symmetrical quartets with two different J- and K-dependent splittings of 30 to 400 kHz in an approximate 3:1 ratio. A set of 22 line centers has been fitted to a symmetric top with rotational constants B, DJ, and $DJK$ of 427.76(2) KHz, 7.2(3) kHz, and 0.869(5) MHz. These results indicate a T-shaped structure having a benzene c.m. to c.m. distance of 4.96 {\AA} and coincident 6-fold and 2-fold axes with a modest effective barrier to internal $rotation.2$ Further work is in progress and the results will be presented.