  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 $\alpha=
2 r_S/b$ 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 $\omega \sim {\mathcal
O}(1/r_S)$. The comparison with previous works and the known literature is
presented.
