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

Photoelectron imaging of the doubly deprotonated ethylenediaminetetraacetic acid dianion (EDTA2–) at variable wavelengths indicates two electron loss pathways: direct detachment and thermionic emission from monoanions. The structure of EDTA2– is also investigated by electronic structure calculations, which indicate that EDTA2– 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 EDTA2– 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.