Observation of an electronic correlation for double Rydberg states of barium

Abstract

Publisher Summary This chapter presents a study of highly excited Nln'l' double-Rydberg states ( D.R.S. ) of barium atom for N = 22 to 34 and n' = 39 to 60 as the principal quantum numbers of the two electrons brought closer together in two ways: (1) n' decreasing toward ν fixed and (2) ν increasing toward n' fixed. In these conditions, the observed spectra trace the evolution from D.R.S. in which the electrons are uncorrelated (N << n) to those in which they are supposed to be (ν ∼ η'). These autoionizing states lie only ∼ 0.1 eV below the double-ionization limit. Their ionic products, which are highly excited Rydberg states of Ba+, are selectively microwave field ionized in Ba2+ before being analyzed by time-of-flight. In the first approach, typical spectra 6snp → 26dn'p and 6snp → 27sn'p for n = 60 to 39 trace the evolution in which the electrons are uncorrelated, showing double-peak structures to the limit N ∼ 0.65n' fixed by the emergence of an unstructure weak broad continuum instead of the double-peak resonances. A shift of the resonance structures to the red wavelength compared to the ionic parent lines was observed. In the second approach for the energy range above the 28s inner electron, the appearance of weak normally forbidden two-photon resonances was also observed in the neighborhood of the 6s → 28p and 6s → 25f ionic line position.