1. Naval Research Laboratory, Washington D.C. 20375-5320, Chemistry Department, George Mason University, Fairfax, Virginia, Dipartimento di Fisica and INFM, Università di Pisa, Via Buonarroti 2, I-56127, Pisa, Italy, INFM-CNR-CRS SOFT, Piazzale Aldo Moro 2, I-00185 Roma, Italy, and Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland