Adiabatic quantum tunneling in heavy-ion sub-barrier fusion

The measured fusion barrier distributions for ⁴⁰Ca + ¹⁹²Os, ¹⁹⁴Pt show significant features due to projectile excitation, while none are seen for ¹⁶O + ¹⁴⁴Sm. This conflict is reconciled using realistic coupled-channel calculations, which show that the higher excitation energy of the 3⁻ state in ¹⁶O produces an adiabatic potential renormalization, without affecting the structure in the barrier distribution. This result indicates that adiabatic effects restrict, in a natural way, the states which influence the shape of a fusion barrier distribution.