1. Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow East, Glasgow G4 0NG, U.K.
2. STFC Central Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Campus, Didcot OX11 0QX, U.K.
3. WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Technology and Innovation Centre, 99 George Street, Glasgow G1 1RD, U.K.
4. Department of Chemistry and York Biomedical Research Institute, University of York, Heslington, York YO10 5DD, U.K.