Electron impact resonances of uracil in an aqueous environment from anion photoelectron imaging

Abstract

The effect that solvation has on electron attachment to uracil, U, was studied by probing the electronic resonances of the uracil radical anion, U−, in gas-phase water clusters, U−(H2O) n , using photoelectron imaging across a range of photon energies. Specifically, the π 3* shape resonance was probed in detail and the spectral signatures following excitation to this resonance are considered. Several new methods for analysis are provided to capture the different actions of the resonance on the photoelectron emission, which in turn provide insight into the location of the π 3* resonance and its subsequent dynamics. The effect of solvation on each action observed through the photoelectron emission is studied for n ⩽ 10. We find that the actions—be they related to statistical emission, prompt autodetachment, or the photoelectron angular distributions—all become less sensitive as the cluster size increases, suggesting that their use for very large clusters may be limited. Additionally, we consider the correlation between electron detachment from the anion, as probed in the experiments, and electron attachment to the neutral. Specifically, they are linked through the reorganisation energy in a linear response picture and we show how the cluster approach developed here allows one to decompose the total reorganisation energy into intramolecular (associated with the anion to neutral geometry change in U) and intermolecular (associated with the change in hydration sphere) contributions. For U in a bulk aqueous environment, we find that the total reorganisation energy, λ ∼ 1.2 eV, shows equal contributions from both intra- and intermolecular changes.