Recoil ion mass spectrometry: systematic studies of slow, multiply-charged recoil ion production in collisions of fast fluorine ions with Ar and Kr atoms

Abstract

Mass spectrometric studies have been conducted on slow, multiply-charged recoil ions produced in high energy collisions of hydrogenic and helium-like fluorine ions with neutral Ar and Kr atomic beams at impact energies in the range 60–99 MeV. A crossed-beam apparatus incorporating a quadrupole mass spectrometer has been used in conjunction with a heavy-ion accelerator. High recoil ion charge states, up to Kr 14+ and Ar 10+, are observed. These ions possess kinetic energies in the range from thermal to a few hundred millielectronvolts. A comparative study of multiple ionisation by fast ion impact and electron impact at the same collision velocity reveals that the former method results in multielectron ejection with efficiencies which are several orders of magnitude larger than for the electron impact case. Fractional dependences for recoil ion formation in different charge states have been measured for F q+ ( q = 5–8) projectiles; these data indicate that indirect multiple ionisation mechanisms, such as excitation-autoionisation and Auger decay processes, may dominate multielectron ejection in fast ion—neutral collisions. Such processes have hitherto not been taken into account in any theoretical treatment.