Bond stabilization by charge transfer: the transition from Van der Waals forces to the simplest chemical bonds

The passage from Van der Waals interactions to covalent one-electron bonds is documented along the series of monohalides and monoxides of the rare gases: bond stabilizations due to open-shell interaction anisotropies — as experimentally observed from molecular beam scattering of orbitally aligned oxygen and halogen atoms by rare gases and simple molecules — are shown to originate from an electron exchange effect. A semi-empirical correlation rule for this effect is established and extended in order to include also excited states, ionic in nature (the excimer states) and other (pseudo)-one-electron-bound systems, such as the rare-gas dimer ions.