Effects of temperature and wavelength on the primary process in the photo-oxidation of iron(II) ion

Abstract

Experiments at 253.7 and 228.8 nm, each over a range of ca. 45 K, demonstrate that the primary quantum yield of photo-oxidation in deoxygenated acidic iron(II) solutions increases only very slightly with temperature, but that at the lower wavelength it is ca. 1.36 times greater. It is suggested that the excitation process involves the transfer of an electron to a shallow trap among the neighbouring solvent molecules, such that recombination of the electron with its geminate iron(III) ion is highly probable. It appears that temperature has little effect on the quantum yield because electron escape and recombination both depend on temperature to very similar extents and that the use of a higher-energy photon increases the quantum yield because then more and more distant traps are accessible for electron transfer.