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Abstract

We have measured branching fractions for ultraviolet electric dipole transitions from upper levels belonging to the 3d5(6S)4p7P and 3d5(6S)4p5P terms of Mn II. The levels were excited in a hollow cathode lamp and the spectra were observed with a Fourier transform spectrometer. The high signal-to-noise ratio of the Mn II lines in our spectra permitted the measurement of branching fractions even for the weakest transitions in the ultraviolet, which are of particular astrophysical interest. A comparison with previous measurements revealed that many of these measurements, including the most recent, show systematic distortions that may indicate that they are affected by self-absorption. Absolute oscillator strengths, based on the new branching fraction measurements, were determined using existing experimental lifetime data. The uncertainty of the f-values is less than 5% for strong transitions. Oscillator strengths for several very weak intercombination lines with log gf < -2 are reported for the first time.