Ultraviolet absorbance spectra of ferric iron solutions of varying iron concentrations maintained at a constant pH of 1.0 and a constant ionic strength of 0.1 were studied. The experimental conditions of low pH minimized the formation of the hydrolytic FeOH2+ and Fe(OH)2+ species; thus, the spectra of iron solutions containing principally the Fe3+ species were recorded. The digitized spectral data were used to establish a model for the Fe3+ absorption spectrum that involves a Gaussian function with three parameters for each of the two absorption bands. These parameters were the wavenumber of the band maximum, ν‾max, the full width at half maximum intensity, Δν‾1/2, and the absorptivity of the band maximum, ɛmax. This study provided estimates for these parameters at 25°C for 0.1 ionic strength media.
Mary F. Brown and Dana R. Kester, "Ultraviolet Spectroscopic Study of Ferric Iron Solutions," Appl. Spectrosc. 34, 377-380 (1980)