1. Department of Chemistry University of Houston 112 Fleming Building Houston TX 77204‐5003 USA
2. Naval Research Laboratory 4555 Overlook Ave. SW Washington DC 20375 USA
3. Xinjiang Technical Institute of Physics and Chemistry Chinese Academy of Sciences 40‐1 Beijing Road Urumqi Xinjiang 830011 China
4. Department of Materials Science and Engineering Northwestern University 2220 Campus Drive Evanston IL 60208‐3108 USA