1. Departments of Chemistry and Physics, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
2. School of Chemistry and EaStCHEM Research School, University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh, U.K. EH9 3JJ
3. Max Planck Department for Structural Dynamics, Department of Physics, University of Hamburg, Centre for Free Electron Laser Science, DESY, Notkestrasse 85, Hamburg 22607, Germany