Two-center effect on low-energy electron emission in collisions of 1-MeV/u bare ions with atomic hydrogen, molecular hydrogen, and helium:: II.: H2 and He -: art. no. 062724

We have studied the energy and angular distributions of low-energy electron emission in collisions of bare carbon ions of 1-MeV/u energy with He and H-2 targets. The double-differential cross sections (DDCS's) are measured for electrons with energies between 0.5 and 300 eV emitted within an angular range of 15 degrees to 160 degrees. The large forward-backward asymmetry observed in the angular distributions is explained in terms of the two-center effect. Single differential cross sections (SDCS's) and total cross sections are also derived by integrating the DDCS's over emission angles and energies. The data are compared with different theoretical calculations based on the first Born, CDW (continuum-distorted-wave), and CDW-EIS (eikonal-initial-state) approximations. The angular distributions of DDCS's and SDCS's are shown to deviate largely from the predictions of the B1 calculations, and are in much better agreement with both the continuum distorted-wave models. The CDW approximation provides a better agreement with the data compared to the CDW-EIS approximation, especially at higher electron energies. The total ionization cross sections for all three targets are shown to follow a scaling rule approximately.