High-Energy Ion-Atom Collisions pp 46-50 | Cite as

# Electron capture to the continuum

## Abstract

The second-order Oppenheimer-Brinkman-Kramers approximation is used to obtain a simple analytical formula, evaluated to the lowest order in the fine structure constant α in the numerator, for the differential cross section for electron capture to the continuum (ECC) by incident bare ions having velocity v from target hydrogenic atomic systems. Both non-relativistic and relativistic forms are derived. Comparison of the theory with the experimental data of Dahl (1985) and Andersen et al (1986) for H^{+}, He ^{2+} + He collisions is reasonably satisfactory for energies > 50 keV/amu. However, theory shows that although the velocity dependence obtained by Andersen et al is v^{−11.3±0.2} in the range of impact energies 1–2.6 MeV/amu, this does not mean that the asymptotic v^{−11} velocity dependence given by the non-relativistic second-order OBK cross section is nearly attained. In fact it is shown that this cannot happen until an energy > 500 MeV/amu is reached where the effect of relativity produces a significant change in the energy fall off. Also a modification of the second-order OBK approximation obtained by Shakeshaft and Spruch (1978) has been expanded to first order in the atomic number Z_{P} of the projectile ion to get simple formulas for the yield of continuum electrons and the cusp asymmetry factor *β*. The accordance with the data of Andersen et al (1986) is fair at energies > 0.5 MeV/amu/Z_{P} but the situation is uncertain at lower energies since there is disagreement between different experimental groups and CDW theory results in smaller values of *β* than the OBK2 theory.

## Keywords

Atomic Number Impact Energy Differential Cross Section Helium Atom Relativistic Form## Preview

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## References

- Gulyas L, Szabo Gy., Berenyi D, Kover A, Groeneveld K O, Hoffmann D and Burkhard M 1986 Phys Rev A
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