Two-Electron Systems—The Helium Atom

Abstract

The system with two electrons is studied in this chapter. Section XI.1 shows that the space of physical states of the helium atom is the sum of the parahelium and the orthohelium spaces. In Section XI.2 the ionization thresholds (i.e., the energy values E _{n ∞} at which one electron is in the nth level and the other is just dissociating from the atom) are determined, and the energy levels below the first ionization threshold are discussed. Section XI.3 discusses the energy levels above the first ionization threshold without considering the interaction between these levels and the energy continuum of the (He⁺, e) system.