Laboratory Measurement of the Fe<scp>ii</scp>114.4938 Nanometer Oscillator Strength

Abstract

We report a laboratory measurement of the oscillator strength, or f-value, for the far-ultraviolet Fe II resonance transition 3d6(5D)4s a6D9/2-3d5(4G)4s4p(3Po)y6F at λvac = 114.4938 nm. We restructured the High Sensitivity Absorption Spectroscopy experiment at the Synchrotron Radiation Center in Stoughton, WI, to extend its operating range, and measured the f-value for the Fe II 114.49 nm resonance transition relative to well-known reference f-values for two resonance transitions, 3d6(5D)4s a6D9/2-3d5(4S)4s4p(3Po)y6P at λvac = 160.8451 nm and 3d6(5D)4s a6D9/2-3d6(5D)4p z6P at λvac = 234.4214 nm. The Fe II 114.49 nm absorption f-value is 0.083 ± 0.006, 20% to 30% smaller than f-values determined from astronomical observations. The accuracy of our measurement is the direct result of careful control and calibration of experimental parameters, cross-checked by measuring the relative f-values of our two reference lines.