  The stopping power of antiprotons in atomic and molecular hydrogen as well as
helium was calculated in an impact-energy range from 1 keV to 6.4 MeV. In the
case of H2 and He the targets were described with a single-active electron
model centered on the target. The collision process was treated with the
close-coupling formulation of the impact-parameter method. An extensive
comparison of the present results with theoretical and experimental literature
data was performed in order to evaluate which of the partly disagreeing
theoretical and experimental data are most reliable. Furthermore, the size of
the corrections to the first-order stopping number, the average energy
transferred to the target electrons, and the relative importance of the
excitation and the ionization process for the energy loss of the projectile was
determined. Finally, the stopping power of the H, H2, and He targets were
directly compared revealing specific similarities and differences of the three
targets.
