Vacuum Ultraviolet Resonance Absorptionf‐values for Niii

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Abstract
We have used the High Sensitivity Absorption Spectroscopy experiment at the Synchrotron Radiation Center in Stoughton, Wisconsin, to measure relative absorption oscillator strengths, or f-values, for six resonance transitions of Ni+ in the vacuum ultraviolet. This laboratory absorption work is an extension of recent laser induced fluorescence and emission work which established an accurate, absolute scale for Ni II resonance f-values. The relative absorption f-values are normalized using three absolute f-values for Ni II, previously determined by combining experimental radiative lifetimes and emission branching fractions, to produce an expanded set of seven absolute resonance f-values for Ni II. Accurate f-values for Ni II resonance lines are critical to the analysis of spectra on the diffuse interstellar medium and are used to determine various properties of the ISM. Resonance lines of Ni II are also observed in high redshift QSO absorption line systems.