ELECTRON-IMPACT STUDY OF THE 50000 CM-1 BAND OF BENZENE

The 5.7-6.7 eV energy loss region of the electron scattering spectrum of benzene which contains the 50000 cm-1 (2100 A) optical absorption band has been studied with incident energies from 10 to 42 eV, scattering angles from 0° to 15°, and energy resolution from 25 to 35 meV. Three different inelastic processes have been detected including the S2 1B1u←S0 transition whose diffuse vibronic bands extend from 6.0 to 6.7 eV, a process at 6.31 eV which occurs strongly at incident energies above 20 eV and increases in intensity relative to the rest of the spectrum with increasing scattering angle and a weak, featureless process below the onset of the S2←S0 transition starting at 5.67 eV. Aside from the weak process below the onset of the S2 state and a singlet-triplet transition observed at very low impact energy, the electron impact spectrum at incident energies below 20 eV and scattering angles to 15° agrees completely with the optical absorption spectrum. The 6.31 eV process arises from a second electronic state at this energy which causes the apparent shift in vibronic band intensities with scattering angle of the S 2←S0 transition first observed by Lassettre et al. The state responsible for this effect is shown to be the same state observed in two photon absorption by Johnson and assigned as 1E1g or 1E2g. Neither the 6.31 eV process nor any energy-shifted analog of it is observed in toluene - providing additional evidence that the 6.31 eV state is a Rydberg state. © 1979 American Institute of Physics.