1. Institute for Chemical and Bioengineering, ETH Zürich, CH-8093 Zürich, Switzerland
2. Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
3. Max Planck Institute for Dynamics and Self-Organization, D-37073 Göttingen,
Germany
4. Laboratory for
Ultrafast Spectroscopy, EPFL, CH-1015 Lausanne,
Switzerland