  New experimental data on 2+ energies of 136,138Sn confirms the trend of lower
2+ excitation energies of even-even tin isotopes with N > 82 compared to those
with N< 82. However, none of the theoretical predictions using both realistic
and empirical interactions can reproduce experimental data on excitation
energies as well as the transition probabilities (B(E2; 6+ -> 4+)) of these
nuclei, simultaneously, apart from one whose matrix elements have been changed
empirically to produce mixed seniority states by weakening pairing. We have
shown that the experimental result also shows good agreement with the theory in
which three body forces have been included in a realistic interaction. The new
theoretical results on transition probabilities have been discussed to identify
the experimental quantities which will clearly distinguish between different
views.
