Electron-ion coincidence study of ionizing thermal energy collisions between He*(21S) and Ar atoms

Abstract

Ionization in thermal energy collisions between excited He*(21S) and ground state Ar atoms leads to final states involving a free electron and either dissociating He–Ar+(2P3/2,1/2) (PI) or bound HeAr+(2P3/2,1/2) molecular ion states (AI). The higher-lying initially bound HeAr+(2P1/2) levels may be subject to predissociation to unbound He−Ar+(2P3/2) states with release of kinetic energy. By means of coincidence studies of the mass-selected ions and the energy-resolved electrons in conjunction with quantum mechanical calculations of the PI and AI processes we show that essentially all of the initially bound HeAr+(2P1/2) levels are predissociated over the ion detection time of 4 µs.