The ion-ion collision processes in dense. high-temperature plasma are investigated. We focus upon the antiscreening channels of the excitation of a one-electron target by a one-electron projectile. In a pseudopotential framework, we take into account plasma-screening effects as well as quantum effects of diffraction and symmetry. The semiclassical straight-line trajectory method is applied to the ion projectile path in order to calculate transition probabilities and cross sections. It is a well-known fact that screening reduces the transition probabilities of the bare collision process. In contrast to this, the quantum effects incorporated here lead to an enhancement of the transition probabilities. In this paper, we study how these effects compete.