The electronic structures and binding tendencies X2, XX', HX, and InX (X, X' = F, Cl, Br, I) were studied. The orbital energies are compared with photoelectron spectra calculated with the Koopmans theorem; the phenomena are interpreted, which could not be described rationally in the Schroedinger-equation framework.l

Key words: HALIDE, COMPUTATIONAL METHOD, MOLECULAR ORBIT, ENERGY LEVELS, ELECTRONIC STRUCTURE, BONDING, DIATOMIC MOLECULE, HYDROGEN COMPOUNDS, INDIUM COMPOUNDS, HUCKEL MOLECULAR ORBITAL