CHARGE-CHANGING REACTIONS IN COLLISIONS OF HYDROGEN CATION, HYDROGEN ANION, AND HYDROGEN WITH ATOMIC AND MOLECULAR HYDROGEN (HYDROGEN ATOMS, HYDROGEN IONS, LOW-ENERGY

The projectile-charge-changing cross sections (sigma)(,10) and (sigma)(,-10) have been measured for H('+) and H('-) impact on H and H(,2) targets for projectile energies from 2.0 keV to 0.063 keV. The results are compared with other experimental and theoretical studies of these reactions. For the case of neutral H-atom impact on H targets, the (sigma)(,01) and (sigma)(,0-1) cross sections were measured relative to those for the same reactions with H(,2) targets. These cross-section ratios, together with the known cross sections for H(,2) targets, have allowed the cross sections for H targets to be determined absolutely. These measurements for H + H collisions are the first ever attempted in this low range of interaction energies, and have identified the reaction channel H + H (--->) H('+) + H('-) as the dominant charged-particle-production mechanism at laboratory H energies below about 0.2 keV. The new techniques used to prepare the H-atom targets for the experiments are also described.