  The electron and positron acceleration in the first cycle of a laser-driven
wakefield is investigated. Separatrices between different types of the particle
motion (confined, reflected by the wakefield or ponderomotive potential and
transient) are demonstrated. The ponderomotive acceleration is negligible for
electrons but is substantial for positrons. An electron bunch, injected as
quasi-monoenergetic, acquires a localized energy spectrum with a cut-off at the
maximum energy.
