  With the quantum diffusion approach the behavior of the capture cross-section
is investigated in the reactions $^{92,94}$Mo + $^{92,94}$Mo, $^{100}$Ru +
$^{100}$Ru, $^{104}$Pd + $^{104}$Pd, and $^{78}$Kr + $^{112}$Sn at deep
sub-barrier energies which are lower than the ground state energies of the
compound nuclei. Because the capture cross section is the sum of the complete
fusion and quasifission cross sections, and the complete fusion cross section
is zero at these sub-barrier energies, one can study experimentally the unique
quasifission process in these reactions after the capture.
