Cross Sections for Electron Capture and Loss by Fast Bromine and Iodine Ions Traversing Light Gases

Bromine and iodine ions, accelerated to energies between 6 and 15 MeV, were passed through thin gas targets of ${\mathrm{H}}_2$ and He. Nonequilibrium charge distributions were measured, from which cross sections for capture and loss of one or more electrons by the heavy ions were determined by means of a least-squares fitting technique. The cross sections are discussed with regard to their functional dependence on the charge and velocity of the ions. Owing to the unprecedented precision of the results, characteristic irregularities were revealed in the charge dependence of the cross sections for both capture and loss of one and two electrons. These effects are attributed to the influence of shell structure and residual excitation of the ions.