Electron structure of endohedrally confined atoms: atomic hydrogen in an attractive shell

The properties of hydrogen confined endohedrally at the geometrical centre of a spherical, attractive short-range potential shell are explored. The evolution of the energy spectrum, as a function of the depth of the shell, is found to exhibit unusual level crossings and degeneracies resulting in avoided crossings and a new phenomenon of `mirror collapse' where the localized states switch places. In addition, a new level ordering, principally by the number of nodes in the radial wavefunction, develops. The results apply generally to endohedrally confined atoms. Further, they suggest a new tool for controlling the properties of atoms.