Photoexcitation of free and bound nucleons

The excitation of nucleon resonances in the second resonance legion formed by the P-11(1440), the D-13(1520), and the S-11(1535) resonances by eta- and pi(o) photoproduction is reviewed. Photoproduction of eta-mesons in the energy range of interest is dominated by the excitation of the S-11(1535) resonance while pi(o)-production involves a strong contribution from the D-13(1520) resonance. In a series of experiments carried out st the MAMI accelerator with the TAPS detector the photoproduction of neutral mesons has been measured on the proton, the deuteron, on C-12, Ca-40, Nb-93 and Pb-nat. The new experimental results allow to study the elementary process on the free proton, to extract information about the cross section on the neutron by exploiting quasifree meson production on denterium, and to investigate possible medium modifications of the resonances in complex nuclei.