Core scattering of quadratic Zeeman orbits in barium

We report a method to uncover the peaks due to scattering of quadratic Zeeman orbits by the atomic core of a many-electron atom. The method is experimental, and consists in identifying the supernumerary peaks in the scaled-energy spectra by comparing them with the corresponding hydrogenic calculations using closed-orbit theory. The scaled actions of the observed additional peaks correspond to combining the scaled actions of individual closed orbits, except for a small blueshift, which is explainable as a core-induced interaction, depending on the penetration of the orbits. Our method is related to earlier theoretical studies of helium, but can be applied to any experimentally accessible atom, including those with large cores. We show that, for barium, core-scattering processes do indeed occur, and that they are confined to a specific portion of the scaled-energy spectrum.