  The nonlinear fluid theory developed by Schamel suggests a modified KdV
equation to describe the temporal evolution of ion acoustic (IA) solitons in
the presence of trapped electrons. The validity of this theory is studied here
by verifying solitons main characteristic, i.e., stability against successive
mutual collisions. We have employed a kinetic model as a more comprehensive
theory than the fluid one, and utilized a fully kinetic simulation approach
(both ions and electrons are treated based on the Vlasov equation). In the
simulation approach, these solitons are excited self-consistently by employing
the nonlinear process of IA solitons formation from an initial density
perturbation (IDP). The effect of the size of IDPs on the chain formation is
proved by the simulation code as a benchmark test. It is shown that the IA
solitons, in presence of trapped electrons, can retain their features (both in
spatial and velocity direction) after successive mutual collisions. The
collisions here include encounters of IA solitons with the same trapping
parameter, while differing in size. Kinetic simulation results reveal a
complicated behavior during a collision between IA solitons in contrast to the
fluid theory predictions and simulations. In the range of parameters considered
here two oppositely propagating solitons rotate around their collective center
in the phase space during a collision, independent of their trapping
parameters. Furthermore, they exchange some portions of their trapped
populations.
