1. Department of Physics, University of Gothenburg, Origovägen 6 B, 41296 Gothenburg, Sweden
2. Université Gustave Eiffel, COSYS/IMSE, 5 Bd Descartes 77454, Champs sur Marne, France
3. Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK