The FERRUM Project: Experimental oscillator strengths of the UV 8 multiplet and other UV transitions from the y6P levels of Fe II

We report on experimental branching fractions (BFs) for 19 transitions from the three 3d5(6S)4s4p(3P) y6P levels in Fe II, measured in Fourier transform spectra of a Penning discharge lamp and a hollow cathode lamp. The transition wavelengths span the interval between 1600 and 2850 Å. Absolute oscillator strengths ( f -values) have been derived by combining the BFs with experimental radiative lifetimes recently reported in the literature. Theoretical f -values have been calculated using configuration interaction wavefunctions. The new experimental and theoretical f -values are compared with data available in the literature and in databases. The strongest lines measured belong to the UV 8 multiplet of Fe II, which has one ground state transition appearing as a prominent feature at 1608 Å in interstellar spectra. The line is accompanied by a satellite at 1611 Å due to a level mixing, which is discussed in the paper.