1. Department of Chemistry, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland
2. A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
3. Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, 12489 Berlin, Germany
4. Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom