  The space-charge effect, due to the instantaneous emission of many electrons
after the absorption of a single photons pulse, causes distortion in the
photoelectron energy spectrum. Two calculation methods have been applied to
simulate the expansion during a free flight of clouds of mono- and bi-energetic
electrons generated by a high energy pulse of light and their results have been
compared. The accuracy of a widely used tool, such as SIMION(R), in predicting
the energy distortion caused by the space-charge has been tested and the
reliability of its results is verified. Finally we used SIMION(R) to take into
account the space-charge effects in the simulation of simple photoemission
experiments with a time-of-flight analyzer.
