Charge-Exchange Collisions between Metastable Hydrogen Atoms and Iodine Molecules

Beams of hydrogen atoms in the ($2S$) metastable state and ground state were passed through an iodine vapor target at energies between 0.2 and 2.5 keV. Measurements of the positive-ion current after the iodine target indicate that the cross section for ionization of the metastable atoms by iodine is much larger than the cross section for ionization of ground-state atoms, especially at the lower energies. The results indicate that this reaction can be effectively used for production of polarized protons in a Lamb-shift polarized-ion source.