RYDBERG STATES IN ELECTRIC AND MAGNETIC-FIELDS - NEAR-ZERO-ENERGY RESONANCES

Several experiments on Rydberg series of atoms in electric and magnetic fields have shown a pattern of equally spaced resonances around the ionisation limit. A unified picture, giving characteristic spacings and their dependence on the external fields is presented. Such patterns of equally spaced levels near zero energy are to be expected quite generally in physics when there is mixing of fields. Further experiments in atoms and in the analogous system of image-potential-induced states at the surface of liquid helium are suggested.