  Intriguing quantum effects that result from entangled molecular rovibrational
states are shown to provide a novel means for controlling both differential and
total collision cross sections in identical particle diatom-diatom scattering.
Computational results on elastic and inelastic scattering of para--H$_2$ and
para--H$_2$ are presented, with the collision energy ranging from 400 cm$^{-1}$
to the ultracold regime. The experimental realization and possible extension to
other systems are discussed.
