Measurements of cross sections for the formation of Mg2+ions by collisions between protons and Mg+

Cross sections for the formation of Mg 2+ by collisions between protons and Mg + have been measured at barycentric energies between 0.98 and 44.5 keV. For energies between 3 and 20 keV the cross section is approximately constant at 7*10 -16 cm 2 although some small structure can be resolved. Below 20 keV there is remarkably close agreement between these measurements and the earlier calculation by Bates et al. (1964) for the process Mg 2+ +H to Mg + +H + . Evidence is presented to indicate that impact ionisation of Mg + is insignificant below 20 keV and so the measurements are believed to refer almost exclusively to the near-resonant charge exchange between protons and Mg + .