  The angular and frequency characteristics of the gravitational radiation
emitted in collisions of massless particles is studied perturbatively in the
context of classical General Relativity for small values of the ratio
$\alpha\equiv 2 r_S/b$ of the Schwarzschild radius over the impact parameter.
The particles are described with their trajectories, while the contribution of
the leading nonlinear terms of the gravitational action is also taken into
account. The old quantum results are reproduced in the zero frequency limit
$\omega\ll 1/b$. The radiation efficiency $\epsilon \equiv E_{\rm rad}/2E$
outside a narrow cone of angle $\alpha$ in the forward and backward directions
with respect to the initial particle trajectories is given by $\epsilon \sim
\alpha^2$ and is dominated by radiation with characteristic frequency $\omega
\sim {\mathcal O}(1/r_S)$.
