Photoelectron photofragment coincidence spectroscopy of carboxylates.

Photoelectron-photofragment coincidence (PPC) spectroscopy is a powerful technique for studying the decarboxylation dynamics of carboxyl radicals. Measurement of photoelectron and photofragment kinetic energies in coincidence provides a kinematically complete measure of the dissociative photodetachment (DPD) dynamics of carboxylate anions. PPC spectroscopy studies of methanoate, ethanoate, propanoate, 2-butenoate, benzoate, p -coumarate and the oxalate monoanion are reviewed. All of the systems studied undergo decarboxylation via a two-body DPD channel i.e. , driven by the thermodynamic stability of CO 2 . Additionally, decarboxylation is observed via a three-body ionic photodissociation channel for p -coumarate. In some cases photodetachment also results in a stable carboxyl radical (RCO 2 ). The branching ratio for DPD, the threshold detachment energy and the peak of the kinetic energy release spectrum are compared for different carboxylates, as a probe of the character of the potential energy landscape in the Franck-Condon region.