1. Département
de Chimie Physique, Université de Genève, Quai E.
Ansermet 30, CH-1211 Genève 4, Switzerland
2. Department
of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
3. Photon
Science Directorate, Brookhaven National Laboratory, Upton, New York 11973-5000, United States