Experiments were carried out at the Linac Coherent Light Source and the Advanced Light Source, both National User Facilities operated respectively by Stanford University and the University of California on behalf of the US Department of Energy (DOE), Office of Basic Energy Sciences. We acknowledge support from the DOE through the PULSE Institute at the SLAC National Accelerator Laboratory; the Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344; the Center for Bio-Inspired Solar Fuel Production, an Energy Frontier Research Center funded by the DOE, Office of Basic Energy Sciences (award DE-SC0001016); the Hamburg Ministry of Science and Research and the Joachim Herz Stiftung, as part of the Hamburg Initiative for Excellence in Research (LEXI); the Hamburg School for Structure and Dynamics; the Max Planck Society, for funding the development and operation of the CAMP instrument within the ASG at CFEL; the US National Science Foundation (awards 0417142 and MCB-1021557); the US National Institutes of Health (awards 1R01GM095583-01 (ROADMAP) and 1U54GM094625-01 (PSI:Biology)); the Swedish Research Council; the Swedish Foundation for International Cooperation in Research and Higher Education; Stiftelsen Olle Engkvist Byggmästare; the DFG Cluster of Excellence at the Munich Centre for Advanced Photonics; and the CBST at the University of California under cooperative agreement no. PHY 0120999. We acknowledge discussions with M. Rossmann, E. Snell, R. Stroud and A. Brunger, thank B. Hedman, E. Gullikson, F. Filsinger, A. Berg, H. Mahn and C. Kaiser for technical help and thank the staff of the LCLS for their support in carrying out these experiments.