Electron energy loss under scattering by complex organic compound vapors

Low-energy electron scattering by anthracene and 1,4-di 2-(5-phenyloxazolyl)-benzene (POPOP) vapors at low pressures is studied. The primary electron beam energy E0 was varied between 10 and 60 eV. The scattering angle was theta = 900. It has been found that in the electron-energy-loss spectra, bands with maxima of 3.7 and 5.41 eV for anthracene, 4.02 and 7 eV for POPOP correspond to the S0→S1 and S0→S2 transitions. Low intensity electron-energy loss due to T2-states excitation has been observed in the region of 2.15 eV for anthracene and 2.54 eV for POPOP. From comparison with optical absorption spectra and analysis of spectra structure changes at different E0 the nature of other bands has been determined. From the obtained results it was concluded that the probability of T1-state excitation is low. It is shown that the main mechanism of populating the T1-state by electric methods of vapor pumping is the process of intersystem crossing