RECOIL ION MASS-SPECTROMETRY .2. FORMATION OF SLOW, MULTIPLY-CHARGED RECOIL IONS IN COLLISIONS OF FAST NEGATIVE-IONS WITH AR AND KR ATOMS

Mass spectrometric studies have been conducted on slow, multiply charg ed recoil ions produced in collisions of O-, Si-, C- and C2- ions with neutral beams of Ar and Kr atoms at impact energies in the range 40-7 0 keV. A crossed-beams apparatus incorporating a quadrupole mass spect rometer has been coupled to the mass-selective negative ion injection system of a tandem heavy-ion accelerator for these studies. In contras t to the situation pertaining to multiple ionisation in collisions wit h fast positively charged projectiles, where indirect ionisation mecha nisms, such as excitation-autoionisation and Auger rearrangement proce sses may dominate multielectron ejection, the dependence of the relati ve multiple ionisation cross sections on the nature of the projectile species,in the present experiments appears to indicate that in ionisat ion by negative ions, the overall electron density distribution in the projectile-target system may play a very significant role.