In an experiment carried out in a linear, unmagnetized plasma, evoluti
on and propagation of nonlinear, rarefactive ion-acoustic pulses have
been investigated. The nonlinear rarefactive pulse is observed to unde
rgo fissioning as it propagates. Measurements of the ion velocity dist
ribution function within the pulse indicate strong modifications of th
e distribution functions at velocities in the neighbourhood of the ion
acoustic speed. Wave-particle interaction is thus shown to play an im
portant role in the observed behaviour. Large-amplitude rarefactive pu
lses, while showing multiple fissioning, also exhibit a large-amplitud
e, low-frequency (approximate to 30 kHz) oscillatory tail, downstream
of the main pulse. The oscillatory tail is unlike the expected Airy fu
nction that normally accompanies a weakly nonlinear rarefactive pulse.
The observations suggest the existence of ion-hole-like structures on
the downstream side. The mechanism of the excitation seems to be thro
ugh modification of the ion phase space due to trapping of ions in the
negative potential well of the rarefactive pulse.