  A three-center phenomenological model able to explain, at least from a
qualitative point of view, the difference in the observed yield of a
particle-accompanied fission and that of binary fission was developed. It is
derived from the liquid drop model under the assumption that the aligned
configuration, with the emitted particle between the light and heavy fragment
is obtained by increasing continuously the separation distance, while the radii
of the light fragment and of the light particle are kept constant. During the
first stage of the deformation one has a two-center evolution until the neck
radius becomes equal to the radius of the emitted particle. Then the three
center starts developing by decreasing with the same amount the two tip
distances. In such a way a second minimum, typical for a cluster molecule,
appears in the deformation energy. Examples are presented for $^{240}$Pu parent
nucleus emitting $\alpha$-particles and $^{14}$C in a ternary process.
