Absorption Cross Sections and Photoionization Efficiencies of Benzene and Styrene Vapor in the Vacuum Ultraviolet

Absorption cross sections and photoionization efficiencies of benzene and styrene vapor have been measured in the wavelength regions of 600–2200 Å and of 600–1000 Å, respectively. Strong absorption peaks ascribed to the π-electron transition 1 A 1g → 1 E 1u have been observed at 1790 Å for benzene and at 1960 Å for styrene. Corresponding oscillator strengths are 0.91 and 0.62, respectively. A strong and broad continuum with its maximum at about 700 Å has been observed for both benzene and styrene; cross sections around the maximum are 140 and 180 in unit of 10 -18 cm 2 , respectively. Energy-loss spectra for styrene vapor have been deduced from the present results and compared with previous data on the solid polystyrene. It is pointed out on the basis of the above results, that the transitions at the energy-loss of 6.5–7 eV and of 20 eV can be interpreted as due to a molecular excitation and a photoionization process, respectively, and that the previous assignments as due to collective excitations are unnecessary.