University of Valencia, Faculty of Chemistry, Physical Chemistry Department Avda. Dr. Moliner, 50 C.P. 46100 Burjassot Valencia Research Group SIGMO Signal & Modelling University of Valencia Physical Chemistry Department  Buiding E, third floor Faculty of Chemistry Avda. Dr. Moliner, 50 46100 Burjassot         Valencia       Spain      e-mail: isidro.monzo@uv.es               Phone +34  96 354 33 42  Fax +34 96 354 45 64