Excitation of metastable states of inert-gas atoms by electron impact in the near-threshold energy region

An experimental setup is described for a comprehensive investigation of the energy and angular dependences of the formation of metastable particles by a method in which a gasdynamic molecular beam intersects a monoenergetic electron beam, and results of excitation of the metastable states of inert-gas atoms near the threshold are reported. For helium, neon, and argon atoms, a splitting of the maximum of the angular dependence of the produced metastable particles is observed, and it is suggested that it is due to spatial separation of the atoms in two metastable states. The angular distributions of the metastable particles are shown to depend on the mass of the atom and on the energy of the electron. A resonant structure is observed in the energy dependences of the cross sections for the excitation of atoms into metastable states at various detection angles (observation angles). This structure is due to the contribution of the short-lived states of the negative ion. Special observation angles are found, in which the resonances are most clearly pronounced