Lawrence Berkeley National Laboratory
Mechanism of Ferric Oxalate Photolysis
- Author(s): Mangiante, DM
- Schaller, RD
- Zarzycki, P
- Banfield, JF
- Gilbert, B
- et al.
Published Web Locationhttps://doi.org/10.1021/acsearthspacechem.7b00026
© 2017 American Chemical Society. Iron(III) oxalate, Fe3+(C2O4)33-, is a photoactive metal organic complex found in natural systems and used to quantify photon flux as a result of its high absorbance and reaction quantum yield. It also serves as a model complex to understand metal carboxylate complex photolysis because the mechanism of photolysis and eventual production of CO2is not well understood for any system. 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 find that intramolecular electron transfer from oxalate to iron occurs on a sub-picosecond time scale, creating iron(II) complexed by one oxidized and two spectator oxalate ligands. Within 40 ps following electron transfer, the oxidized oxalate molecule dissociates to form free solvated CO2(aq)and a species inferred to be CO2•-based on the appearance of a new vibrational absorption band and ab initio simulation. 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.