Accelerating multiple scattering of the emitted electrons in collisions of ions with atoms and molecules

Complete text of publication follows. Ionization is one of the fundamental phenomena studied in atomic collision physics. Double differential spectra of electrons ejected in ion-atom and ion-solid collisions provide detailed information about the ionization dynamics. During the past decade special emphasis have been laid on the emission of the fast electrons in collisions of heavy partners. Significantly enhanced emission of fast electrons above the binary encounter energy was observed in both ion-atom and ion-solid collisions. In some cases, the fast electrons have been identified as originated from double or multiple scattering by the projectile and target cores. Since the moving projectile ion is much heavier than the electron, such kind of multiple scattering of the electron also accelerates it. The process is often denoted as Fermi-shuttle acceleration. In the present work, we measured the double differential cross-sections for electron emission in collisions of 700-1500 keV N+ ions with N2, Ne and Ar targets. We studied the target atomic number (ZT) dependence of the yield of the Fermi-shuttle type triple and quadruple scattering in these collisions. We performed classical trajectory Monte-Carlo calculations for the target ionization. Figure 1 compares the present experimental double differential cross sections with the results of the CTMC calculation for electron emission at 30 deg, 90 deg and 150 deg in 0.75 MeV N+ + Ar collisions as a function of the ejected electron energy. The experimental double differential cross-sections are in good agreement with the theoretical values, and all the expected target ionization structures (P, P-T, P-T-P and P-T-P-T) clearly appear in the spectra. We consider the present work as a starting point of a systematic study, a combined experimental and CTMC analysis of a wide range of collision systems. (author)