1. Istituto Strutturistica Chimica and NMR Service of CNR, Area della Ricerca di Roma M.B.10, Monterotondo Stazione, 00016 Rome, Italy; INFM and Department of Physics, University of L'Aquila, V. Vetoio 1, Coppito, 67100 L'Aquila, Italy; Department of Physics, University “La Sapienza”, P. le Aldo Moro 5, 00185 Rome, Italy; and Department of Chemistry, University “La Sapienza”, P. le Aldo Moro 5, 00185 Rome, Italy