1. Institute of Applied Physics of the Academy of Sciences of Moldova, Academy str. 5, Chisinau MD-2068, Moldova, Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77843-3012, and Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306