Radiative-lifetime measurements and calculations of odd-parity highly excited levels in Ba i

Abstract

Natural radiative lifetime measurements have been performed for $70$ odd-parity highly excited levels of neutral barium in the energy range from $308$ $15.512$ to $417$ $59.93$ cm${}^{\ensuremath{-}1}$ by a time-resolved laser-induced fluorescence technique in a laser-produced plasma. The lifetime values measured in this paper are in the range from $11.3$ to $901$ ns. They are compared with the published lifetimes of four levels. Two of them are in good agreement, whereas for the other two our measurements are slightly longer than the published data. The reasons for the discrepancies are discussed. Comparisons with theoretical results of the Hartree-Fock method with relativistic corrections illustrate the difficulties associated with the use of Cowan's codes for obtaining accurate branching fractions for transitions depopulating highly excited levels along the Rydberg series of heavy neutral elements. This work will be useful to extend the set of oscillator strengths available in Ba i.