Cross sections for the production of excitedHe+(np)2

Abstract

Cross sections have been measured for the production of He ϩ ͑np) 2 P o states, nϭ2,3,4, by proton impact on helium over a projectile velocity range of 1.42-2.45 a.u. ͑50 рEр150 keV͒. Cross sections were determined by measuring the extreme ultraviolet photons emitted from excited He ϩ ions. The data indicate a lower energy than expected for the maximum cross section. A comparison of the present results in terms of projectile energy dependance with the cross sections for excitation to He ͑1snp) 1 P o , ionization, and total electron capture suggests the primary mechanism for the production of excited He ϩ at low energies is transfer excitation, with ionization excitation being the dominant mechanism at higher energies.

Ionization-excitation of H-and He by Compton scattering

“…Thus we expect that exclusive cross sections for n 5 are not sensitive to electron correlation. The exclusive cross sections n = 3-5 are in approximate agreement with an n −3 dependence (Bransden andJoachain 1983, Stolte andBruch 1996) as shown in figure 6. That is, our exclusive cross sections for n 3 can be fitted approximately by a curve f (n) = C/n 3 , where C is a constant.…”

Ionization–excitation of helium to He (2p) magnetic sublevels following electron, proton, and molecular hydrogen (H2 and H3 ) impact

“…When a negatively or positively charged projectile collides with a helium atom at intermediate to high impact energies, the dominant collision mechanisms are elastic scattering, excitation, and ionization of the target with subsequent emission of photons and/or electrons (Fülling et al 1992, Bailey et al 1995, Stolte and Bruch 1996. Simultaneous ionizationexcitation of the target can also occur at sufficiently high energies, but it leads to relatively small emission cross sections (Bailey et al 1995), thereby making this process very difficult to observe experimentally.…”

Polarization measurements of the extreme ultraviolet (EUV) emission following excitation and ionization-excitation of helium by fast electron, proton, and molecular hydrogen (H 2 + and H 3 +) impact

“…15 When a negatively or positively charged projectile collides with a helium atom at intermediate to high impact energies, the dominant collision mechanisms are excitation and ionization of the target with subsequent detection of photons and/or ejected electrons. 4, 16 The excitation of He (1s 2 ) 1 S to HeI to (1snp) 1 P o (n=2-5) states can principally be formed by the reaction channel:…”