Photoelectron spectroscopy on ionic liquid surfaces - Theory and experiment

We have studied various ionic liquids by photoemission spectroscopy. For a more in depth interpretation of the experimental results, in particular of valence spectra, a theoretical reconstruction of these spectra by means of density functional theory is desired. In order to obtain correct binding energies and peak intensities a simple calculation of the density of states is not sufficient. A self-developed method, which bases on known elementary cross sections for the photoeffect and adjustments of the kinetic energy of emitted electrons, is applied. Particular attention is paid to the necessary relative shift for a cation and anion due to their different Madelung potentials. In order to study this effect, we have varied the cations and the anions of the ionic liquids under investigation, systematically. (C) 2014 Elsevier B.V. All rights reserved.