E. Pollack

Electron capture by simple ions

Publisher Summary Electron-capture collisions are important in plasmas where capture by singly as well as multiply charged ions generally occurs to excited levels, which subsequently decay by radiation emission resulting in energy losses by the system. The capture channels must be included in modeling astrophysical problems and also in addressing a large number of chemical processes because these channels strongly compete with the reactive scattering. Electron capture is generally investigated experimentally by: (1) the energy dependence of the total cross section; (2)the probability of electron capture (or charge exchange) as a function of scattering angle at fixed energy or as a function of energy at a fixed scattering angle; (3) the doubly differential cross section for excitation of a particular outgoing channel; (4) the optical-emission cross section as a function of energy; (5) photon-scattered atom coincidence measurements; and (6) analysis of recoiling target ions or dissociation fragment. Furthermore, the electron-capture processes primarily yield dissociating (or predissociating) states of the molecular ion leading to the production of recoil atoms and atomic ions. In collision systems where a quasi-resonant channel is available the cross section for electron capture is large and the quasi-resonant channel is dominant in the small-angle exchange scattering.

Experimental test of a scaling law for ion-molecule collisions: Ne+-D2, 1.5-3.5 keV

Energy losses are measured for 1.5-3.5 keV Ne+ ions scattered by D2 through angles out to 5 degrees. The results show that the effective scattering mass of a molecule is a function only of the reduced scattering angle tau =E theta , in agreement with a recent scaling theorem by Sigmund (1978).

A data acquisition system for electrostatic energy analyzers

An interface system has been developed which enables rapid acquisition of data from an electrostatic energy analyzer by a multichannel analyzer. Sample data from inelastic ion‐molecule collisions demonstrate its capabilities.