SCALED-ENERGY SPECTROSCOPY OF BARIUM AUTOIONIZING RYDBERG ATOMS IN ANELECTRIC-FIELD

Spectra of Ba autoionizing Rydberg states (n = 60-80) in a varying ext ernal electric held, keeping the classical scaled energy epsilon const ant, have been measured. Series converging to the 5d(3/2)- as well as to the 5d(5/2)-limit have been studied for three values of the scaled energy: epsilon = -2.94, -2.35 and -1.76, deep in the n-mixing regime around the classical held ionization limit (epsilon = -2.0). The exper iments are interpreted using semiclassical closed-orbit theory by taki ng the Fourier transform of the experimental spectra. High resolution is obtained using CW laser excitation and large frequency scans. Effec ts of the large non-hydrogenic core of Ba an: investigated by comparin g the experimental Fourier spectra with hydrogenic closed-orbit theory for m(l) = 0-3 incorporating the 5d(2) (1)G(4) metastable ground-stat e wavefunction and assuming only 5d-nf excitation.