Oscillations of the charge exchange cross sections and the average equilibrium charge of helium ions

The electron loss and capture cross sections for helium ions at velocities v = 8-20 x 108 cm s-1 in helium, nitrogen, neon and argon have been measured and the electron capture cross sections for He+ and He2+ ions in various media have been theoretically calculated in the Oppenheimer-Brinkman-Kramers approximation. It has been found that the dependence of the electron capture cross section on the nuclear charge of the target atoms is oscillating. This phenomenon is caused by the analogous oscillations of the values of the equilibrium charge fraction and the average charge of the fast ions. (author)