  The quasiparticle time blocking approximation (QTBA) is applied to describe
E1 excitations in the even-even tin isotopes. Within the model pairing
correlations, two-quasiparticle (2q), and 2q*phonon configurations are
included. Thus the QTBA is an extension of the quasiparticle random phase
approximation to include quasiparticle-phonon coupling. Calculational formulas
are presented in case of neutral excitations in the spherically symmetric
system. The main equations are written in the coordinate representation that
allows to take into account single-particle continuum completely. The E1
photoabsorption cross sections have been calculated in nuclei 116,120,124Sn. It
has been obtained that the 2q*phonon configurations provide noticeable
fragmentation of the giant dipole resonance resulting in appearance of
significant spreading width. The results are compared with available
experimental data.
