1. Department of Chemistry, Norwegian University of Science and Technology, NTNU, 7491 Trondheim, Norway
2. Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, SDU, Campusvej 55, 5230 Odense, Denmark
3. Department of Chemistry, Technical University of Denmark, DTU, Kemitorvet Bldg 207, 2800 Kongens Lyngby, Denmark
4. Department of Physics, Stockholm University, 10691 Stockholm, Sweden