O. B. Shpenik, M. M. Erdevdy, P. P. Markush, J. E. Kontros, and I. V. Chernyshova, “Electron Impact Excitation and Ionization of Sulfur, Selenium, and Tellurium Vapors”, Ukr. J. Phys., vol. 60, no. 3, p. 217, Jan. 2019.