Qstructure and Inner-Shell Vacancies in Neon-Neon and Krypton-Krypton Collisions

Abstract

In close encounters of the systems Ne-Ne, Ne + -Ne, and Ne ++ -Ne, electrons of 750-eV energy are produced. The numbers of such fast electrons are found to depend upon the charge state of the incident particle (0,+l, or +2) in the ratio of 0.6, 1.0, and 2.0, respectively. This agrees in part with a prediction by Lichten. In Kr + -Kr collisions, there is a sudden change in the average number of electrons lost for 9° scattering at 25-keV incident energy.Previous studies have shown that 200-keV Ne + ions incident upon neon gas cause ejection of 750-eV electrons . l > 2 Coincidence measurements 3 at the same energy showed that there are two distinct values of the average inelastic energy loss Q, one at 710 eV and the other at 1550 eV, for the reaction Ne + + Ne^Ne 5+ +Ne 3+ + 7e (1) with the scattering angle 6 set at 8°. These two results suggested 3 that a K-shell vacancy can be created by such collisions. Lichten 4 drew energy-level diagrams for the Ne-Ne system and made a qualitative explanation in terms of a K-shell promotion mechanism. He predicted that the number of fast electrons should be dependent upon the charge of the incident neon, in the ratio of 0, 1, and 2 for Ne, Ne + , and Ne ++ , respectively.Our experiment is performed to check Lichten's prediction. Here Ne, Ne + , and Ne ++ of 200-keV energy are sent through neon gas. Previously described apparatus and procedures 5 are used to make a (noncoincident) energy analysis of the resulting fast electrons and later to determine (with coincidence methods) the Q values at 10° scattering. Figure 1(a) shows the electron energy distributions, normalized to the same incident-particle flux per unit target gas density, for the three different cases. The data are taken with electrons scattered at 95° to the incident direction, this angle chosen to prevent scattered neons from reaching the detector and to limit Doppler broadening (see Ref.

Double effects of projectile charge state on Nb L-shell ionization by slow highly ionized Xe ions

“…A significant enhancement for ionization cross sections is observed within q ≤ 19, and in this stage, the 4d hole number of Xe q+ ions (q 4d (q)) varies from four to a maximum of 10. This growth trend is in excellent agreement with the prediction of the electron promotion model [5,13]. For higher charge states, unexpectedly, ionization cross sections decrease dramatically with increasing charge states.…”

“…For slow nearly symmetric or fully symmetric collisions, electron promotion with coupling molecular orbitals allows a successful qualitative description of this effect [11][12]. Within this scheme, target ionization cross sections increase with each additional incident vacancy [5] (e.g., Ne K-shell electron promotion probability ratio induced by Ne ++ , Ne + , and Ne are 2 : 1 : 0.6) [13].…”

Experimental Study of the Effect of Velocity and Outer-Shell Configuration on the Probability for ProducingKVacancies in Violent Ion-Atom Collisions at keV Energies

“…The upper curve, obtained with 300-keV doubly charged Ne ions, shows that for fixed r 0 and impact velocity, P n is almost twice as high for Ne ++ -Ne collisions as for Ne + -Ne collisions. This charge-state effect, originally predicted by Lichten, 3 has been studied previously by McCaughey et al 9 They showed that KLL Auger-electron yields for Ne ++ -Ne collisions were about twice as high as those for Ne + -Ne collisions. For symmetric collisions, Lichten 3 successfully introduced the concept of diabatic MO correlations which are based essentially on the MO correlations of the H 2 + one-electron diatomic system.…”

Collisional X-Ray Excitation in Solid and Gaseous Targets by Heavy-Ion Bombardment

“…1 ' 2 It is to be expected that the probability of L electron transfer to a higher shell depends on the number of empty levels available in that shell. 3 " 5 At a given ion energy, the excitation state of outer shells and, thus, the number of unoccupied levels therein, may be varied by passing the ion through a solid or a gaseous target. The average charge state, e.g., of a 40-MeV I ion in a gas target is ~ 10+ (cf.…”