Using particle-in-cell computer simulation, the processes occurring in a plasma formed by isothermal evaporation of ions and electrons off a planar wall are studied. A simple model to implement three-body recombination is introduced into this scheme; it fulfills momentum and energy conservation and obeys the well-known dependences of the recombination rate on density and temperature. Ion acceleration processes are investigated, during both the particle emission phase and afterwards, during expansion into vacuum. Recombination strongly enhances ion acceleration, since due to the recombination-heated electron subsystem the expansion-front space-charge field is increased. Spatial segregation of the neutral gas cloud and the plasma cloud is demonstrated.