Transition from quantum to quasi-classical behaviour of the binary encounter peak in collisions of 0.6 to 3.6 MeV amu-1 I23+ and Xe21+ with He and Ar

Abstract

Double differential cross sections are reported for the production of binary encounter electrons in collisions of 0.6 MeV amu-1 I23+ and 1.4, 2.4, and 3.6 MeV amu-1 Xe21+ projectiles incident on He and Ar targets. Electron energy spectra were measured between 0 degrees and 45 degrees in the case of the two lower projectile energies, and between 17.5 degrees and 60 degrees for the two higher projectile energies. The data are compared with quantum mechanical impulse approximation and classical trajectory Monte Carlo calculations. While the quantum model calculation predicts a rapid disappearance of diffraction effects in the binary encounter peak with increasing projectile energy, these remain visible in the experimental results up to the highest energy measured. The necessity of including multiple target ionization involving inner shell electrons in the theoretical description of the collision process is demonstrated by the classical trajectory Monte Carlo calculation, which accounts well for the shape of the 2.4 and 3.6 MeV amu-1 cross sections, except at angles where diffraction effects are manifest. Systematic shifts of the binary encounter peak position towards lower energies with increasing emission angle were observed for all projectile energies.