Cross sections for charge exchange to continuum levels of protons

Absolute cross sections for the process of charge exchange to the continuum for protons incident on molecular hydrogen, helium, neon and argon have been measured in the energy range 300 to 1200 keV. The velocity spectra of electrons ejected in the forward direction are measured and a characteristic cusp-shaped peak is found for electrons ejected with velocity equal to that of the incident protons. Both the shape of the cusp and the absolute cross sections for the yield of electrons within the peak are compared with the theoretical values predicted by Dettmann (J. Phys. B. Atom. Molec. Phys.; 7:269 (1974)) in a second Born approximation to this special type of charge exchange. Provided the background signal beneath the cusp is first subtracted from the experimental results the agreement with peak shape is excellent and the observed cross section, although smaller than predicted, approaches the theoretical energy dependence, E-5, at high energies. In principle, however, the theory should include this background. (author)