Enhancement of Forward-Angle Cross Sections in Heavy-Ion Reactions because of Projectile Excitation

It is shown that the forward-angle cross section in heavy-ion reactions can be strongly enhanced by indirect processes in the projectile or outgoing nucleus. This is demonstrated specifically for the reaction ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$)${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ at 100 MeV, where data for the relevant transitions exist. At the lower energy of 60 MeV, which is just above the barrier, the effect on the forward cross section vanishes but at large angles beyond the peak the cross section is reduced in agreement with experiment.