Characteristic electron emission in the production of Ar2+ by H+ impact on Ar

We have measured recoil ions in coincidence with electrons emitted at 90 deg. with respect to the beam direction, in collisions of 50, 120 and 210 keV H+ on Ar. For these energies the ratio between the yields of the recoil ions Ar2+ and Ar+, as a function of electron velocity, presents a distinctive peak at a velocity close to that of the projectile. Data with neutral projectiles H0, in contrast, do not show such a structure. Measurements with He+ and He0 projectiles on Ar at 25 keV u-1 were also performed, confirming that the characteristic structure is associated with the projectile net charge. (author). Letter-to-the-editor