Uniform properties of J(pi) = 1(-) two-phonon states in the semimagic even-even tin isotopes Sn-116,Sn-118,Sn-120,Sn-122,Sn-124

Systematic nuclear resonance fluorescence experiments including model-indep endent parity determinations provided clear evidence for strong, isolated E l excitations at excitation energies of 3.3-3.5 MeV in the spherical, semim agic nuclei Sn-116.118,Sn-120,Sn-122,Sn-124, The corresponding J(pi) = 1(-) states are interpreted as two-phonon excitations (2(+)circle times 3(-)). The excitation energies E-x(1(-)) and reduced excitation probabilities B(E1 )up arrow are nearly constant in the entire isotopic chain ri = 116-124. Th e results are described in the framework of quasiparticle-phonon-model calc ulations. [S0556-2813(99)00704-9].