Projectile and target excitation in He^(+)+He collisions at intermediate energies

We present ab initio calculations of cross sections for projectile and target excitation occurring in the course of He^(+)+He collisions using a threeactive-electron semiclassical nonperturbative approach.Intermediate impact energies ranging from 1 keV to 225 keV/u are considered.The results of our calculations agree well with available measurements for both projectile and target excitation in the respective overlapping energy regions.A comparison of our results with those of other theoretical calculations further demonstrates the importance of a nonperturbative approach that includes a sufficient number of channels.Furthermore,it is found that the cross sections for target excitation into singlet states show a valley centered at about 25 keV/u,resulting from competition with electron transfer to singlet projectile states.By contrast,the cross sections for target excitation into triplet states do not exhibit any such structures.