Experimental radiative lifetimes, branching fractions, and oscillator strengths for LaII and a new determination of the solar lanthanum abundance

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