  Positive and negative ions forming so-called pair plasma differing in sign of
their charge but asymmetric in mass and temperature support a new acoustic mode
where damping of heavier ion dominates. The condition for the excitation of ion
sound wave through electron beam induced Cherenkov instability is also
investigated. This beam can generate a perturbation in the pair ion plasmas in
the presence of electrons when there is number density, temperature and mass
difference in the two species of ions. Basic emphasis is on the focusing of ion
sound waves and we show how, in the area of localization of wave energy, the
density of pair particles increases while electrons are pushed away from that
region. Further, this localization of wave is dependent on the shape of the
pulse. Considering the example of pancake and bullet shaped pulses, we find
that only the former leads to compression of pair ions in the supersonic regime
of the focusing region. Here possible existence of regions where pure pair
particles can exist may also be speculated which is not only useful from
academic point of view but also to mimic the situation of plasma (electro
positron asymmetric and symmetric) observed in astrophysical environment.
