Charge Exchange Cross Sections of Hydrogen Ions in Gases

Abstract

Measurements are reported of the cross section for electron capture (${\ensuremath{\sigma}}_{10}$), electron loss (${\ensuremath{\sigma}}_{01}$), and electron detachment (${\ensuremath{\sigma}}_{\ensuremath{-}10}$) for hydrogen atoms and ions traversing several gases. (${\ensuremath{\sigma}}_{\mathrm{if}}$ represents the cross section for charge transfer from initial state $i$ to final state $f$.) The kinetic energy of the particle was from 3 kev to 200 kev. The target gases used were ${\mathrm{H}}_{2}$, He, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, Ne, and A. Cross sections were determined by measuring the attenuation of the hydrogen beam in a gas cell under the influence of an electrostatic or magnetic field. The fraction of the beam in each charge state after passing through a "thick target" was also determined. This latter measurement served as a test for internal consistency of the data, since the fraction is relatable to the cross section for entry to and exit from the charge state. The loss cross section, ${\ensuremath{\sigma}}_{01}$, increased monotonically at low energies, reaching a maximum at a velocity approximately equal to the orbital electron velocity. For the higher energies studied the capture cross section could be represented by an expression of the form, $\ensuremath{\sigma}=A{e}^{\ensuremath{-}bv}$, where $A$ and $b$ are constants for each gas studied. The electron attachment cross section, ${\ensuremath{\sigma}}_{0\ensuremath{-}1}$, was of the order ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$/gas atom for the gases studied and attained a maximum between 5 and 20 kev. The inverse transition, ${\ensuremath{\sigma}}_{\ensuremath{-}10}$, was approximately ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$/gas atom in the energy range studied.