[en] Cross sections have been calculated for single ionization in collisions between protons and helium atoms, in the range of projectile energies 25-100keV. The semiclassical impact parameter method was employed, with basis comprising 22 states on the (He) target and 29 states on the projectile. Good agreement is obtained with the experimental measurements. The inclusion of pseudo-continuum states on the helium centre is found to significantly modify the total cross section for capture into the bound states of hydrogen, leading to improved agreement with the measurements. (author)