Multichannel-quantum-defect theory wave functions of Ba tested or improved by laser measurements

Abstract

Considerable efforts have been made recently to understand the detailed structure and properties of high Rydberg states of the bound even-parity spectrum of Ba. Interest in Ba is motived by the ability to study interacting Rydberg series. The perturbations of 6snl Rydberg series by 5d7d levels are reflected not only in the level structure but also in various observable quantities recently investigated by high-resolution laser spectroscopy. A wealth of data has been obtained on lifetimes, isotopes shifts, Lande factors, hyperfine structures, photoelectron angular distributions, etc. Previously the multichannel-quantum-defect theory (MQDT) has permitted one successfully to interpret the energies of perturbed series. The new possibilities offered by laser spectroscopy to analyze state mixing have provided an opportunity to probe the MQDT wave functions. This paper shows how the data provided by different measurements complement one another to check or even extend the MQDT models derived from energies. Various examples concerning the perturbed 6sns and 6snd Rydberg series are presented. For the 6snd1,3D2 series, energies are insufficient to get the full MQDT parameters needed to determine the wave functions, and gJ-factor and hyperfine-structure measurements have been essential to improve MQDT wave functions.