1. Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, Materials Science and Chemistry Divisions, Argonne National Laboratory, Argonne, Illinois 60439, Department of Chemistry, University of Chicago, Chicago, Illinois 60637, Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130