Oxalate, C2O42-, a plant- and fungi-derived organic acid, forms strong complexes with iron(III) to form a highly photoactive species [1]. Although the photolysis of ferric oxalate, Fe(III)(C2O4)33- has been extensively studied [2,3], the mechanism has until now not been clearly established. We employed pump/probe mid-infrared transient absorption spectroscopy to study the photolysis reaction of the iron(III) oxalate ion in D2O and H2O up to 3 ns following photoexcitation. We tracked the formation and fate of reaction intermediates and determined the reaction pathway [4]. Quantum and classical chemical modeling aided identification of the carbon dioxide radical anion, CO2●—, through a new vibrational band and predicted that this species remains coordinated to the iron(II) product. This work provides direct spectroscopic evidence for the first mechanistic steps in the photolysis reaction and presents a technique to analyze other environmentally relevant metal carboxylate photolysis reactions.

Mechanism of ferric oxalate photolysis from ultrafast infrared spectroscopy

255th National Meeting (2018)

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