The six lowest excited states of benzene have been investigated in the gashyphen;phase free molecule at low pressure by electronhyphen;impact spectroscopy. Incident electron energies of 13.6 and 20.0 eV and scattering angles from 9deg; to 80deg; were used. Three singletndash;singlet transitions at 5.0, 6.2, and 6.9 eV were identified. These transitions agree with the results of optical absorption and higherhyphen;energy electronhyphen;impact experiments. In addition, three triplet states were observed at 3.9, 4.7, and 5.6 eV. The positions of the first two triplet states agreed with optical data on solid benzene and threshold electronhyphen;impact experiments. The third triplet state at 5.6 eV was assigned on the basis of the relative intensity of the transition at various scattering angles. The ratio of the intensity of this transition to the allowed singletndash;singlet transition at 6.9 eV was in a constant proportion to the corresponding ratio for the first triplet state (3.9 eV) at all scattering angles. The spacings of the first and second and second and third triplet states in benzene were determined to be 0.80 and 0.85 eV. The difference in the spacing is not significant with respect to experimental error.
展开▼
