PHOTOCHEMISTRY OF AQUEOUS IRON(III) POLYCARBOXYLATE COMPLEXES - ROLESIN THE CHEMISTRY OF ATMOSPHERIC AND SURFACE WATERS

Photochemical redox reactions of Fe(III) complexes of polycarboxylates (e.g., citrate, malonate, oxalate) occur on time scales of minutes in sunlight and are potentially important sources of Fe(II), .O2-/HO2., H2O2, and .OH in atmospheric water drops and surface waters. Quantum y ields for Fe(II) formation, determined from experiments and equilibriu m speciation calculations, are (i) 0.28 for Fe(OH)(citrate)- at 436 nm , (ii) 0.027 for Fe(malonate)2- at 366 nm, and (iii) 1.0 for Fe(oxalat e)2- and 0.6 for Fe(oxalate)3(3-) at 436 nm. Competitive reactions of O2 and Fe(III) with the polycarboxylate radicals and/or the carbon-cen tered radicals derived from decarboxylation, as well as the speciation of Fe(II) and Fe(III), affect the experimental quantum yields of Fe(I I) formation.