1. G. P. Wiederrecht, Chemistry Division, Argonne National Laboratory, Argonne, IL 60439-4831, USA.
2. B. A. Yoon, Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.
3. M. R. Wasielewski, Chemistry Division, Argonne National Laboratory, Argonne, IL 60439-4831, and Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.