Experimental Radiative Lifetimes, Branching Fractions, and Oscillator Strengths for La ii and a New Determination of the Solar Lanthanum Abundance

Abstract

Radiative lifetimes, accurate in most cases to +/-5%, from time-resolved laser-induced fluorescence measurements on a slow beam of lanthanum ions are reported for 31 odd-parity levels of La II. Experimental branching fractions for La II from emission spectra covering the near-ultraviolet to the near-infrared are also reported. The spectra were recorded using the US National Solar Observatory 1.0 m Fourier transform spectrometer. The branching fractions are combined with the radiative lifetimes to produce 84 experimentally determined transition probabilities or oscillator strengths, generally accurate to +/-10%, for La II. These new experimental results are compared to older experimental and theoretical results. These data are applied to determine a new value for the solar photospheric lanthanum abundance, =1.13, with estimated internal errors of +/-0.03 and external errors of +/-0.03.