Electron capture in the collision of mass-selected hydrogen-cluster ions with helium atoms

The electron capture cross sections of hydrogen-cluster ions H-n(+) colliding with atomic helium have been measured in a large range of cluster size (5 less than or equal to n less than or equal to 35) for the same velocity (1.5v(0), 60 keV/u). While the electron-capture cross section decreases from the H+ ion to the H-3(+) one, the cluster electron-capture cross section is found to be independent of the cluster size and nearly equal to the capture cross section of the H-3(+) ion. The electron capture by hydrogen clusters on a helium atom is a process involving only the H-3(+) core of the cluster when the positive charge is localized. It appears that this very localized electron capture is not disturbed by the presence of molecules, up to 16, around the H-3(+) core. [S1050-2947(98)09511-0].