Excitation of two interacting electrons as a plasmon-decay mechanism in proton-aluminum collisions

Projectile-induced plasmon excitation in an electron gas has been studied by several authors who proposed two possible mechanisms for these plasmons to decay. In a previous work we considered one of these mechanisms in which the plasmon transfers its energy to a nearly free electron that makes an interband transition. In this paper, the other mechanism is analyzed. A simple model is developed to describe plasmon decay in aluminum via the excitation of two interacting electrons. Results for the transition probability and the excitation power are presented. When contributions from both mechanisms are considered, they account for more than 60% of the excited plasmons. Also, the slope of the plasmon excitation curve is correctly reproduced. The study of first and second differential spectra in angle and energy show that plasmon decay into two interacting electrons is the main source of low-energy electrons moving in the forward direction (with respect to the projectile initial velocity).