Inelastic collisions between ions and atoms

Charge-exchange cross-sections for H+, D+, O+2, H+2, O+, CO+ and N+2 in A; D+, O+ and N+ in Kr; D+, C+ and Br+ in Xe, and O+ in H2O have been measured between 25 and 4000 eV energy by a method previously described. The normal atomic collision cross-sections rise to a maximum at a voltage which depends on the value of ΔE √M for the process, M being the atomic mass and ΔE the energy defect of the reaction. Collisions between negative ions and atoms have been studied with the same apparatus, the cross-section of the detachment reaction X- + Y → X + e + Y — ΔE being obtained. For S-, Br-, I-, C-, P-, Li- in Ne, and H- in He, Ne, A, Kr, Xe, this rises with increasing energy of the incident ion. For O- in He, Ne, A, Kr, Xe, Cl- in He, Ne, A, Kr, Xe, and F- in Ne, Kr, Xe the cross-section at low energies is unexpectedly large for the value of ΔE √M. This may be interpreted as being due to the presence of excited states of these ions, of low electron affinities, in the beam. With O-, a low energy electron bombardment source gave smaller cross-sections, i.e. a smaller proportion of excited ions.