1. Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala, Sweden
2. Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden
3. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom
4. Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden