1. Department of Chemistry, University of Helsinki, P.O. Box 55, A. I. Virtasen aukio 1, FIN-00014 Helsinki, Finland
2. Hylleraas Centre
for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, P.O.
Box 1033 Blindern, N-0315 Oslo, Norway
3. Centre for Advanced Study at the Norwegian Academy of Science and Letters, Drammensveien 78, N-0271 Oslo, Norway