1. Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
2. Physics Department, Jagiellonian University, Ul. Prof. St. Lojasiewicza 11, 30-348 Krakow, Poland
3. Paul Scherrer Institute, 5232 Villigen, Switzerland
4. Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland