[1] Univ Paris 11, Lab Phys Solides, CNRS, UMR 8502, F-91405 Orsay, France
[2] Sincrotrone Trieste SCpA, I-34012 Trieste, Italy
[3] Purdue Univ, Dept Chem, W Lafayette, IN 47907 USA
[4] Univ Roma La Sapienza, CNR, IOM, I-00185 Rome, Italy
[5] Univ Roma La Sapienza, Dipartimento Fis, I-00185 Rome, Italy