Electronic capture by [Formula Presented] from atomic and molecular hydrogen

We present absolute measurements of electron-capture cross sections in atomic and molecular hydrogen by [Formula Presented] particles with energies ranging from 0.5 to 2.75 MeV. The measured single-electron-capture cross sections as well as the ratio [Formula Presented] are compared with several available theories. In particular, a detailed analysis of the role played by two-electron processes in the single-electron capture of [Formula Presented] is performed considering a distorted-wave model as a starting point. © 2000 The American Physical Society.