1. Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
2. College of Letters and Science, University of California, Los Angeles, California 90095, United States
3. Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway
4. Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
5. Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Via Elce di Sotto, 8, 06123 Perugia, Italy
6. Max Planck Institute for the Structure and Dynamics of Matter and Center Free-Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany
7. Scuola Normale Superiore, Piazza dei Cavalieri, 7, 56124 Pisa, Italy