Chemistry, Lights and Dynamics Seminar

The electron loss and dissociation dynamics of some complex carboxylate anions, including a dianion, an organic dye molecule and a dicarboxylic acid, have been studied using photoelectron and fragment spectroscopies. Firstly,  the fluorescein dianion (Fl2-) is investigated by photoelectron imaging and secondary mass spectroscopy.1, 2 Electron loss is observed via resonant tunnelling through two distinct repulsive Coulomb barriers (RCB1 and RCB2), which link different excited dianion (S1 and S2) and anions states (D0 and D1), as well as direct photodetachment. This is the first experimental observation of resonant tunnelling mediated via a highly excited electronic state (≥ S2). The primary decarboxylation pathway is the ready loss of CO2 from the relatively short-lived intermediate excited state, Fl-[D1], which is formed by electron loss from the dianion via resonant tunnelling through RCB2. Secondly the oxalate monoanion (HO2CCO2-), the conjugate base of the simplest dicarboxylic acid, is studied using a more detailed experimental technique: photoelectron photofragment coincidence spectroscopy. Following excitation at 266 nm a highly repulsive dissociative photodetachment is observed, resulting exclusively in e- + HOCO + CO2. Moving forward these projects motivate the development of a methodology capable of studying the dissociation dynamics of complex ions in detail.3   

1.          Gibbard, J. A.; Verlet, J. R. R., Kasha’s Rule and Koopmans’ Correlations for Electron Tunnelling through Repulsive Coulomb Barriers in a Polyanion. J. Phys. Chem. Lett. 2022, 13 (33), 7797 - 7801. 

2.          Gibbard, J. A.; Verlet, J. R. R., Unravelling the decarboxylation dynamics of the Fluorescein dianion using secondary mass spectrometry. Submitted 2023. 

3.          Gibbard, J. A.;  Castracane, E.;  Shin, A. J.; Continetti, R. E., Dissociative photodetachment dynamics of the oxalate monoanion. Phys. Chem. Chem. Phys. 2020,22 (3), 1427-1436.