Susan Perkin1, Barbara Kirchner2, Michael D Fayer3. 1. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom. 2. Mulliken Center for Theoretical Chemistry, Universität Bonn, Beringstr. 4, D-53115 Bonn, Germany. 3. Department of Chemistry, Stanford University, Stanford, California 94305, USA.