1. Institute of Physical and Theoretical Chemistry University of Würzburg Am Hubland 97074 Würzburg Germany
2. Present Address: Laboratory for Astrophysics Leiden Observatory Leiden University 2300 RA Leiden (The Netherlands
3. Present address: Department of Dynamics of Molecules and Clusters J. Heyrovský Institute of Physical Chemistry Dolejškova 2155/3 182 23 Praha 8 Czech Republic
4. Laboratory for Synchrotron Radiation and Femtochemistry Paul Scherrer Institut (PSI) 5232 Villigen Switzerland