1. Institute of Physical and Theoretical ChemistryUniversity of Bonn Wegelerstr. 12 53115 Bonn Germany
2. Kekulé Institute of Organic Chemistry and Biochemistry Gerhard-Domagk-Str. 1 53121 Bonn Germany
3. Mulliken Center for Theoretical ChemistryUniversity of Bonn Beringstr. 4 53115 Bonn Germany