Planetary atoms

A planetary atom is an atom or ion in a state, with two or more excited electrons, which has negligible overlap with the ground state or first few excited states. Classical mechanics and Einstein-Brillouin-Keller quantization are used to study them. They are not produced by direct (one-photon) optical excitation from low states, statistically they predominate over states which can be produced by direct optical excitation, and they are long-lived. Each state is a member of a series labelled by a half-odd-integer scaling number ν. The states of the series have energies which are approximately proportional to 1/ν2. The energies of the states of a planetary atom depend on the charge of the parent ion, and not on its detailed structure. Electron energy loss spectroscopy is a possible means of studying planetary atoms experimentally. (author)