1. Department of Physical Chemistry, Uppsala University, Box 579, 751 23 Uppsala, Sweden, Departments of Organic Chemistry and Structural Chemistry, Stockholm University, 106 91 Stockholm, Sweden, Department of Chemistry, Technical University of Denmark, Building 201, Kemitorvet, DK-2800 Lyngby, Denmark, and Department of Analytical Chemistry, Uppsala University, Box 599, 751 24 Uppsala, Sweden