The Argon Release for Controlled Studies (ARCS) 4 sounding rocket was launched northward into high altitude from Poker Flat Research Range on February 23, 1990. The vehicle crossed geomagnetic field lines containing discrete auroral activity. An instrumented subpayload released 100 eV and 200 eV Ar+ ion beams sequentially, in a direction largely perpendicular to both the local geomagnetic field and the subpayload spin axis. The instrumented main payload was separated along field lines from the beam-emitting subpayload by a distance which increased at a steady rate of ~2.4 m s-1. Three-dimensional mass spectrometric ion observations of ambient H+ and O+ ions, obtained on board the main payload, are presented. Main payload electric field observations in the frequency range 0--16 kHz, are also presented. These observations are presented to demonstrate the operation of transverse ion acceleration, which was differential with respect to ion mass, primarily during 100-eV beam operations. The preferential transverse acceleration of ambient H+ ions, as compared with ambient O+ ions, during the second, third, fourth, and fifth 100-eV beam operations, is attributed to a resonance among the injected Ar+ ions, beam-generated lower hybrid waves, and H+ ions in the tail of the ambient thermal distribution. This work provides experimental support of processes predicted by previously published theory and simulations. ¿ American Geophysical Union 1995