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Abstract
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 EO was varied between 10 and 60 eV. The scattering angle was θ = 90°. 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 SO → S1 and So → 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 EO 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.
The development of free complex molecule spectroscopy under electric excitation is hindered by the lack of systematic reliable information about elementary interactions of electrons and other particles with such molecules. When excited in electric discharge or by an electron beam, the complex molecule may be in both a neutral and an ionized state. The investigation of such nonequilibrium gas system presents great difficulties due to a large number of possible elementary processes responsible for excitation, ionization, recombination, dissociation of complex molecules. To develop a kinetic model of such a system, one must know a number of cross sections or rate constants of elastic and inelastic electron collisions with the complex molecule. Unfortunately, such data are practically unavailable.
The aim of the present paper is to obtain information about probabilities of complex molecule singlet and triplet states excitation in a gas phase as a result of collision with low-energy electrons (less than 50 eV).
Most accurate data on effective cross sections of molecule (atom) collisions with electrons are provided by using an electronic spectrometer in which an electron beam with small energy spread (of the order of tens of in electron-energy-loss spectra, S2-state excitation cross sections have a considerably greater value.