  We examine numerically the post-merger regime of two Schwarzschild black
holes in non head-on collision. Our treatment is made in the realm of
non-axisymmetric Robinson-Trautman spacetimes which are appropriate for the
description of the system. Characteristic initial data for the system are
constructed and the Robinson-Trautman equation is integrated using a numerical
code based on the Galerkin spectral method. The collision is planar, restricted
to the plane determined by the directions of the two initial colliding black
holes, with the net momentum fluxes of gravitational waves confined to this
plane. We evaluate the efficiency of mass-energy extraction, the total energy
and momentum carried out by gravitational waves and the momentum distribution
of the remnant black hole. Our analysis is based on the Bondi-Sachs four
momentum conservation laws. Head-on collisions and orthogonal collisions
constitute, respectively, upper and lower bounds to the power emission and to
the efficiency of mass-energy extraction by gravitational waves. The momentum
extraction and the pattern of the momentum fluxes, as a function of the
incidence angle, are examined. The momentum extraction characterizes a regime
of strong deceleration of the system. The angular pattern of gravitational wave
signals is also examined. They are typically bremsstrahlung for early times
emission. Gravitational waves are also emitted outside the plane of collision
but this component has a zero net momentum flux. The relation between the
incidence angle of collision and the exit angle of the remnant closely
approximates a relation for inelastic collisions of classical particles in
Newtonian dynamics.
