Electron Loss and Dissociation Pathways of a Complex Dicarboxylate Dianion: EDTA²

Photoelectron imaging of the doubly deprotonated ethylenediaminetetraacetic acid dianion (EDTA^2-) at variable wavelengths indicates two electron loss pathways: direct detachment and thermionic emission from monoanions. The structure of EDTA^2- is also investigated by electronic structure calculations, which indicate that EDTA^2- has two intramolecular hydrogen bonds linking a carboxylate and carboxylic acid group at either end of the molecular backbone. The direct detachment feature in the photoelectron spectrum is very broad and provides evidence for a dissociative photodetachment, where decarboxylation occurs rapidly after electron loss. Near 0 eV kinetic energy electrons are only observed in the photoelectron spectrum of EDTA^2- at hν = 3.49 eV (high laser fluence), providing evidence for secondary electron loss via a two-photon process, mediated by an excited state of the decarboxylated anion, and likely resulting in a cyclic neutral product.