Atomic collisions in secondary ion production by hydrogen near the electronic stopping power maximum

H+ projectiles from a 2.5 MV van de Graaff accelerator were used to bombard a carbon target (500 Angstrom) under high vacuum conditions. By varying th e H+ projectile energy (50-160 keV/u) it was possible to scan the low energ etic Lindhard-Scharff-Schiott region (LSS), the maximum, and the high energ etic Bethe-Bloch region (BB) of the electronic stopping power (dE/dx)(e). T he secondary ion yields Y(H+C2Hx+, C3Hx+, C4Hx+, C5Hx+) from the beam entra nce surface were measured with a time of flight spectrometer (TOF). The mea surements reveal a non-linear behaviour between the electronic stopping pow er (dE/dx)(e) calculated with TRIM, in the maximum and the Bethe-Bloch regi on, and the secondary ion yields. However, the experimental results show go od agreement with a new Pereira et al. [Int. J. Mass Spectrom. Ion Proc. 17 4(1998) 179] effective energy loss model. (C) 1999 Elsevier Science B.V. Al l rights reserved.