1. LPCNO, Université de Toulouse, INSA, UPS, LPCNO, 135 Avenue de Rangueil, F-31077 Toulouse, France, and CNRS, LPCNO, UMR 5215 CNRS-UPS-INSA, F-31077 Toulouse, France
2. Institut Charles Gerhardt, Université Montpellier 2, Avenue E. Bataillon, F-34095 Montpellier, France, and CNRS, Institut Charles Gerhardt, F-34095 Montpellier, France
3. Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460