Electron-Atom Scattering: The State of the Experiments

Abstract

The state of the experiments in low-energy electron-atom scattering is reviewed as part of the proceedings of the second George J. Schulz Symposium. Particular emphasis is placed on those experimental investigations that require a high electron energy resolution, such as studies of narrow resonances and threshold excitation and ionization processes.

Collisional electron capture to the continuum of neutral projectiles

“…The scattering of low-energy electrons by excited atoms represents an important elementary process in dense plasmas, but it is extremely difficult to study under ordinary laboratory conditions (Schulz 1973, Read 1983. The present work suggests that coincidence measurements of electron capture to the continuum of neutral atoms in atomic collisions, where the ejected electron can move with arbitrarily small velocities relative to the projectile, may provide an alternative method for extracting experimental information on low-energy electron-excited atom collisions.…”

“…Our conjecture is that the experimentally observed ECC peak for neutral projectiles (Sarkadi et a1 1989) is associated with the presence of a low-lying virtual state for the electron-projectile system. For instance, in the case of neutral helium, there is abundant evidence about a low-lying virtual state of the e-He system, when the helium core is in a metastable 2lS excited state (Burke et a1 1969, Oberoi and Nesbet 1973, Schulz 1973, Berrington et a1 1975, Nesbet, 1975, Fon et a1 1978, VuEiC et a1 1981, Read 1983. We attribute the experimentally observed ECC peak to a sizable fraction of excited 2lS states already present in the incoming beam or possibly produced during the collision.…”

“…In this sense, the ECC peak observed by Sarkadi et a1 (1989) may represent a very interesting manifestation in atomic physics of a virtual state. The information in other rare-gas and alkali atoms is far more limited than in the case of He (Schultz 1973, Read 1983, Buckman et al 1983, Bae and Peterson 1985, and similar measurements for such systems should be highly desirable.…”