Energy spectra of forward-ejected electrons in multiple ionization of Ar by 1 MeV protons

Time-of-flight (TOF) techniques have been used to measure singly and multiply ionized Ar recoils in coincidence with energy-analysed, forward-ejected electrons in 1 MeV H + -Ar collisions. Electron energies up to 2800 eV and charge states 1-4 are covered. It is shown experimentally that the peak of binary-encounter (BE) electrons in the electron energy spectrum is associated almost entirely with single ionization of Ar, whereas the peak of electron-capture-to-the continuum (ECC) electrons is associated with multiple ionization. This shows that the BE electrons originate exclusively from the valence shell of Ar (the M shell) and the ECC electrons predominantly from an inner shell (the L shell).