  The collision of plane waves corresponding to massless states of closed
string is considered in $D$-dimensional space-time. The reduced tree level
effective action is known to be manifestly $O(d,d)$ invariant, $d$ being the
number of transverse spatial dimensions in the collision process. We adopt a
coset space reformulation of the effective two dimensional theory and discuss
the relation of this process with classical integrable systems in two
dimensions in the presence of gravity. We show how it is possible to generate
new backgrounds for the scattering process, from known background solutions to
the equations of motion, in the coset reformulation. We present explicit
calculations for the case of four space-time dimensions as an illustrative
example.
