Proton-neutron structure of collective excitations in P. von Brentano, C. Fransen, A. Gade, A. Lisetskiy and N. Pietralla Eur. Phys. J. A, 13 1-2 (2002) 99-103 Published online: 15 January 2002 DOI: 10.1140/epja1339-16