Inelastic Processes of Electron Interaction with Chalcogens in the Gaseous Phase (a Review)

Complex research of elementary pair collision processes occurring when low-energy (0–70 eV) electrons pass through chalcogen (S, Se, Te) vapor has been carried out in the evaporation temperature intervals of those elements (T = 320÷700 K for sulfur, 420÷490 K for selenium, and 400÷600 K for tellurium). The vapor compositions of indicated elements are studied using the mass spectroscopy method. The radiation spectra are analyzed in the wavelength interval from 200 to 600 nm with the help of optical spectroscopy. Using highly monoenergetic electron beams, the total (integral) formation cross-sections for positive and negative S, Se, and Te ions are measured. It is found that, under the experimental conditions, the main components of chalcogen vapor are molecules containing 2 to 8 atoms. At the energies of bombarding electrons below 10 eV, the emission spectra mainly consist of bands of diatomic molecules, and, at higher energies (E > 15 eV), there appear separate atomic and ionic lines. At E = 50 eV, the lines of singly charged ions are the most intense ones. It is shown that the most effective reaction channel is the interaction of electrons with diatomic molecules of indicated elements, whereas other processes are mainly associated with the decay of polyatomic molecules. The excitation and ionization thresholds for interaction products are found by analyzing the energy dependences of process characteristics. Specific features are also observed in the energy dependences of the excitation and ionization functions. Doubly charged ions of diatomic sulfur molecules, as well as selenium and tellurium atoms, are revealed for the first time. The appearance of triply charged ions of diatomic sulfur molecules is also detected. The main contribution to the total (integral) effective ionization cross-section of both positive and negative ions is proved to be made by the interaction processes of electrons with diatomic molecules S2, Se2, and Te2. Besides the experimental research, a detailed theoretical study is carried out. Calculations with a theoretical analysis of their results are performed for the structural characteristics of homoatomic sulfur, Sn, selenium, Sen, and tellurium, Ten, molecules with n = 2÷8; namely, interatomic distances, ionization potentials, electron affinity energies, and dissociation energies. The energy characteristics are applied to calculate the appearance energies for singly and doubly charged ionic fragments of those molecules at the dissociative ionization. The obtained results are carefully compared with the available experimental and theoretical data.