Cations Strongly Reduce Electron-Hopping Rates in Aqueous Solutions

Summary, in English

We study how the ultrafast intermolecular hopping of electrons excited from the water O1s core level into unoccupied orbitals depends on the local molecular environment in liquid water. Our probe is the resonant Auger decay of the water O1s core hole (lifetime similar to 3.6 fs), by which we show that the electron-hopping rate can be significantly reduced when a first-shell water molecule is replaced by an atomic ion. Decays resulting from excitations at the O1s post-edge feature (similar to 540 eV) of 6 m LiBr and 3 m MgBr2 aqueous solutions reveal electron-hopping times of similar to 1.5 and 1.9 fs, respectively; the latter represents a 4-fold increase compared to the corresponding value in neat water. The slower electron-hopping in electrolytes, which shows a strong dependence on the charge of the cations, can be explained by ion-induced reduction of water-water orbital mixing. Density functional theory electronic structure calculations of solvation geometries obtained from molecular dynamics simulations reveal that this phenomenon largely arises from electrostatic perturbations of the solvating water molecules by the solvated ions. Our results demonstrate that it is possible to deliberately manipulate the rate of charge transfer via electron-hopping in aqueous media.

• Author: Niklas Ottosson; Michael Odelius; Daniel Spangberg; Wandared Pokapanich; Mattias Svanqvist; Gunnar Öhrwall; Bernd Winter; Olle Bjorneholm
• Department/s: MAX IV Laboratory
• Publishing year: 2011
• Language: English
• Pages: 13489-13495
• Publication/Series: Journal of the American Chemical Society
• Volume: 133
• Issue: 34
• Links: http://dx.doi.org/10.1021/ja204100j
• Document type: Journal article
• Publisher: The American Chemical Society (ACS)
• Topic: Natural Sciences; Physical Sciences
• Status: Published
• ISBN/ISSN/Other: ISSN: 1520-5126