Magnetic ''wave trapping'' and what is termed here electric ''phase bunching'' are shown to be the high and low energy behaviors which result when a magnetized heavy ion interacts with a nearly resonant electromagnetic cyclotron wave. The properties of electric ''phase bunching'' are explored by computer simulation. Because these properties match observations it is concluded that the strongly cyclotron phase bunched and energized helium ions, observed in association with waves in the earth's geostationary magnetosphere, are generated by this electric ''bunching'' process.