Oscillator Strengths for Astrophysics: Advances in Ultraviolet and Vacuum Ultraviolet Measurements
Advanced techniques for measuring oscillator strengths of ultraviolet (UV) and vacuum ultraviolet (VUV) transitions are presented. Oscillator strengths (f-values) are determined in a combination of three experiments. Radiative lifetimes measured using time-resolved laser-induced fluorescence provide the absolute normalization required to convert emission branching fractions or relative absorption oscillator strengths into absolute f-values. Branching fractions are measured using "classic" and Fourier transform spectroradiometry on optically thin sources. Relative absorption oscillator strengths are measured in a newly developed high sensitivity absorption experiment. These advanced techniques are superior to older techniques in reliability and accuracy. This dissertation describes the first laser-based f-value measurement of the Si II 180.801 nm transition, of the Cr II "triplet" near 206 nm, and of the Zn resonance transitions near 204 nm; the first laboratory measurement of the Fe II 160.845 nm transition, and new accurate experimental determinations for f-values of the Fe II resonance transitions at 224.918 and 226.008 nm, and the Si II intersystem transitions near 235 nm. In addition, extensive radiative lifetime measurements are reported for Ti II, Ni I, and Co I which dramatically extend the knowledge of accurately measured radiative lifetimes for the iron group elements.
- Pub Date:
- January 1995
- LASER INDUCED FLUORESCENCE;
- Physics: Atomic