Highly Excited Barium Rydberg Atoms in External Electric, Magnetic, and Combined Fields

We have observed Rydberg states of barium with principal quantum numbers up to n = 520 in zero external fields. At lower principal quantum numbers we have studied barium Rydberg atoms in external electric, magnetic, and parallel fields. Because of the effective suppression of stray electric fields we have observed quasi-Landau resonances in external magnetic fields in the order of tens of Gauss. The energy dependence of the spacing between neighboring quasi-Landau resonances was found to be in excellent agreement with calculations involving classical trajectories. In addition the Stark effect of the n = 46, |m| = 0, 1, 2 diamagnetic manifolds has been investigated. The recorded spectra clearly exhibit the influence of the non-hydrogenic part of the Coulomb potential of the ionic core. The observed line positions and intensities have been accounted for by diagonalizing the corresponding Hamiltonian in a truncated spherical basis set.