The results of a numerical simulation of the O+ energization perpendicular to the magnetic field (B) in electrostatic shocks with converging or diverging fields at altitudes ~2000 km are presented. It is shown that non-adiabatic motion in diverging shocks leads to the formation of coherent perpendicular O+ beams, whereas converging fields produce non-Maxwellian tails and heating of core ions. In both cases, ion energization is accompanied by the formation of spatially narrow density dips. Inside these dips, double layers may easily be formed resulting in electron acceleration upwards or downwards depending on whether the electric field diverges or converges. The results are in qualitative agreement with relevant observations. ¿ 1998 American Geophysical Union