Photodetachment of Deprotonated R-Mandelic Acid: The Role of Proton Delocalization on the Radical Stability.

The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O …H … OCO) features a single local minima, with the proton localized on the O group (OH… OCO). However, the structure with the proton localized on the OCO group (O …HOCO) is also observed because it falls within the extremity of the vibrational wavefunction of the OH… OCO isomer along the PT coordinate. The stability of the corresponding radicals, produced upon photodetachment, is strongly dependent on the position of the proton in the anion: the radicals produced from the OH… OCO isomer decarboxylate without barrier, while the radicals produced from the O …HOCO isomer are stable.