  Mutual collisions between ion-acoustic (IA) solitary waves are studied based
on a fully kinetic simulation approach. Two cases, small and large relative
velocity, are studied and the effect of trapped electron population on the
collision process are focused upon. It is shown that, for the case of small
relative velocity, the repelling force between the trapped populations of
electrons results in scattering of electron holes. However, this phenomenon can
not be witnessed if the relative velocity is considerably high, since the
impact of trapped population stays very weak.
