Hyperfine structure and isotope shifts in odd-parity 6snp and 6snf Rydberg series of Ba I

Abstract

Hyperfine structure and isotope shifts in transitions to odd-parity 6snp and 6snf Rydberg configurations of barium have been investigated using laser-atomic-beam spectroscopy. For the 6snf Rydberg configurations with n=13-42 the complete hyperfine multiplet is observed. The data on isotope shifts have been used to test the total perturber character mixed in the 6snp and 6snf Rydberg states predicted by existing multichannel quantum defect theory (MQDT) treatments of the odd-parity J=0, 1, 2, 3 and 4 spectra. The MQDT predictions are shown to be reliable in this respect. The hyperfine structure of the singlet and triplet states is analysed in terms of singlet-triplet mixing. The extracted mixing coefficients disagree with the predictions of existing MQDT models, even when an interaction between 'singlet' and 'triplet' 6snl channels is introduced. New MQDT models have been developed in which both energies and mixing coefficients are reproduced well. Hyperfine structure data provides information on interactions between mutually perturbing channels. Finally an earlier analysis of the hyperfine structure of the 6snf 3F states in terms of effective parameters is discussed.