ABSORPTION SPECTRA OF BENZENE AND BENZENE-$d_{6}$ IN THE VACUUM $ULTRAVIOLET^{*}$

$^{*}$This research was assisted in part by the Office of Ordnance Research under project TB 2-0001 of Contract DA-11-022-ORD-1002 with The University of Chicago. (1) A preliminary account of this work was given in J.Chem. Phys. 24, April (1956)Author Institution: Department of Physics, The University of ChicagoThe absorption spectra of benzene and benzene-$d_{6}$ have been photographed in the $1300^{\circ} A$ to $1800^{\circ} A$ region using the first order of a 21-foot vacuum spectrograph and the zenon and krypton continua as absorption backgrounds. Four Rydberg series were identified in each molecule, converging to ionization potentials of 9.247 ev (benzene) and 9.251 ev (benzene-$d_{6}$). Progressions of the $\nu_{2}, \nu_{18}$ and $\nu_{20}$ vibrations are associated with most of the 31 observed Rydberg transitions. The strong intensity and unusual length of the upper state $\nu_{18}({e}_{2{g}})$ progression in comparison with the $\nu_{2}({a}_{1{g}})$ progression are interpreted in terms of the Jahn-Teller theorem, and it is concluded that the stable equilibrium nuclear configuration in the Rydberg states is of $D_{2{h}}$ symmetry. (1)