“…However, a new feature arises here, namely, oscillating terms in Wz due to the excitation of the real plasmons. In the semiclassical limit [1,3,5,6] oscillations change the profile of the image force energy drastically, having amplitudes comparable with the background classical term W cl z, especially for emitted particles. This behaviour is conserved in the quantum-mechanical theory when the recoil effect is small (the``above-thresholdº situation) [9 to 12].…”