The interaction of inert gases

Abstract The following paper studies from a quantum mechanical point of view a special kind of chemical reaction, namely, the inertness of the inert gases. In the development of the quantum theory of homopolar binding this chapter has hitherto been omitted for the following reason: not only is the charge distribution of an inert gas atom spherically symmetrical, but the whole ψ-function, which depends in the case of n electrons on 3n space co-ordinated and n spin co-ordinates, is invariant under a simultaneous orthogonal transformation of all co-ordinates. This means that there is no space degeneracy. If now this atom is brought near to another similar one, the disappearance of direction symmetry is not followed by a disappearance of degeneracy—the stationary state does not split up into several states as in most cases of chemical binding, but remains single and seems to correspond, under ordinary conditions, to repulsion. On the other hand, Heitler and London in their well-known treatment of the H2-problem, found that it was just the removal of a degeneracy, which they called “exchange degeneracy,” which gave rise to large resonance forces and thus led to binding in one of the resultant states and repulsion in the other. This induced subsequent workers to suppose that the antiparallel copuling of two electron spins in different atoms always entails a binding force. This was supported from the theorectical side by the fact that the interaction energy could actually be worked out as a sum of terms each belonging to such as coupling. Such a theory could not fail to fit the experiments as it established the rules Lewis’ theory of electron pairs—a theory already proved to have wide validity.