1. Centre for Theoretical Chemistry and Physics The New Zealand Institute for Advanced Study Massey University Auckland 0632 Auckland New Zealand
2. Mulliken Center for Theoretical Chemistry University of Bonn Beringstr. 4 53115 Bonn Germany
3. Department for Molecular Theory and Spectroscopy Max-Planck-Institut für Kohlenforschung (KOFO) Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Germany