Multidimensional tunneling description of subbarrier fusion

Abstract

We introduce an alternative method for the exact quantum mechanical treatment of subbarrier fusion, namely the time-dependent wave packet method where a wave packet in the radial and in additional internal collective degrees of freedom of the fusing system is propagated on the multidimensional potential surface. An advantage of the method is to yield a very intuitive picture of the fusion process. It also solves directly a given model for the energy surface without the need to expand in a basis set. In this way we can clearly ascertain the effects of the spreading in the additional degrees of freedom (zero-point-motion and excitation), the dynamics of the motion on the surface, and the tunneling through the barrier. In applying the approach we have considered as a new degree of freedom in subbarrier fusion the formation of a neck and treated it in the adiabatic approximation. Neck formation is found to be very important for the enhancement of fusion giving as much or more enhancement as the deformation effect alone. For the fusion of ⁵⁸Ni + ⁵⁸Ni we are thus able to account very well for the experimenal data.