Since several years the applicant is carrying on some research activity in collaboration with M.V.Andres on (see ref. 13, 14, 21, 24, 26 in the list of publications) a) Dynamical distortion effects in heavy ion collisions b) Multiphonon excitation in grazing heavy ion collisions. One of the scopes of the proposal is to pursue the collaboration on these subjects in a more efficient way and to enlarge it involving other people of the same Department in Sevilla who are already working on the same or related topics (Joaquin Gomez Camacho, Manuel Lozano, ...). A long term visit to Sevilla would also allow the establishment of a collaboration in the broad domain of the Interacting Boson Model (IBM) and its microscopic foundations. In this context, the work done by Jose Arias and Clara Alonso in Sevilla could be complemented by the experience of the applicant. The collective pair approximation (see ref. 1-5, 8, 10, 19, 27) and the mapping procedures (see ref. 20, 23, 25) more recently introduced by the applicant in the study of various many fermion systems, allow on one hand to exploit the simplifications introduced by the basic ideas of the IBM. On the other hand, they allow to take into account the underlying fermionic structure.