1. Department of Chemical Engineering, University of Pennsylvania, 311A Towne Building, 220 S 33rd Street, Philadelphia, Pennsylvania 19104-6393, Molecular Simulations Inc., 9685 Scranton Road, San Diego, California 92121-3752, Grace Davison, 2500 Grace Dr., Columbia, MD 21044, and NIST Center for Neutron Research, Gaithersburg, Maryland 20899-8562