  The overtaking collisions of ion-acoustic solitons (IASs) in presence of
trapping effects of electrons are studied based on a fully kinetic simulation
approach. The method is able to provide all the kinetic details of the process
alongside the fluid-level quantities self consistently. Solitons are produced
naturally by utilizing the chain formation phenomenon, then are arranged in a
new simulation box to test different scenarios of overtaking collisions. Three
achievements are reported here. Firstly, simulations prove the long-time life
span of the ion-acoustic solitons in the presence of trapping effect of
electrons (kinetic effects), which serves as the benchmark of the simulation
code. Secondly, their stability against overtaking mutual collisions is
established by creating collisions between solitons with different number and
shapes of trapped electrons, i.e. different trapping parameter. Finally,
details of solitons during collisions for both ions and electrons are provided
on both fluid and kinetic levels. These results show that on the kinetic level,
trapped electron population accompanying each of the solitons are exchanged
between the solitons during the collision. Furthermore, the behavior of
electron holes accompanying solitons contradicts the theory about the electron
holes interaction developed based on kinetic theory. They also show behaviors
much different from other electron holes witnessed in processes such as
nonlinear Landau damping (Bernstein-Greene-Kruskal -BGK- modes) or beam-plasma
interaction (like two-beam instability).
