Simultaneous excitation and ionisation of helium by fast projectiles

Abstract

The cross sections for simultaneous excitation and ionisation in helium following impact of fast electrons, protons and C"' ( q = 3-6) ions have been investigated by measuring the vacuum-ultraviolet radiation from transitions in He I I (np-1s) in the wavelength region 220-315 A. The cross sections obtained with 500-2000 eV electrons are found to be larger by a factor of 1.4-2.3 than those obtained with protons of the same velocity (0.92-3.76 MeV). The difference is discussed in terms of an interference between two excitation-ionisation mechanisms.

Multielectron Processes in Heavy Ion–Atom Collisions at Intermediate Velocity

“…Until today, very few measurements have been made and then just for light atoms at high velocities [4][5][6][7][8]. Theoretical interpretation remains controversial in terms of correlation effects needed to correct the independent electron model (IEM).…”

Two-electron transitions in high energy ion-helium collisions

“…Very recent measurements [7] of the two-electron process of excitation ionization in helium show the same sort of Zp ---+1 compared to Zp = -1 (electrons) differences as seen in double ionization. On the other hand, recent measurements [8,9] of the two-electron transition to doubly excited resonance states of helium (2s2p~P -k (2p) 2 ID)…”

Ionization-excitation of He by fast proton and antiproton: a QED approach

“…However, the experimental values of the cross sections in die refs. [7] and [8] do not agree among themselves though the ration of the cross sections by negative and positive projectiles lies around 2.…”

“…There are experimental investigations of IE of H2 [6] and He [7,8] by energetic electrons (e") and protons (p+). Antiproton (p') collision of He leading to single ionization (SI) and double ionization (DI) are reported in [9] and [10], respectively.…”