ABSORPTION SPECTRA OF BENZENE AND BENZENE-<i>d</i>₆ IN THE VACUUM ULTRAVIOLET

Abstract

The absorption spectra of benzene and benzene-d 6 have been photographed from 1300 Å to 1850 Å in the first order of a 21-ft. normal incidence vacuum spectrograph. The band analysis resulted in the identification of four Rydberg series (over one hundred vibrational bands) in each molecule, converging to ionization potentials of 9.247 ev. (benzene) and 9.251 ev. (benzene-d 6 ). Progressions of the ν 2 , ν 18 , and ν 20 vibrations are associated with most of the 31 observed Rydberg transitions, and vibrational constants are tabulated for each. The strong intensity and the unusual length of the upper state ν 18 (e 2g ) progression in comparison with the ν 2 (a 1g ) 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 2h symmetry.