Electron Capture Processes Following Collisions of He$^{2+ }$ Ions with Molecular Targets

Energy-gain spectra, absolute state-selective and total cross sections have been measured for single-electron capture processes in collisions of He$^{2+}$ ions with O$_{2}$, H$_{2}$O, CO$_{2}$, N$_{2}$, and NH$_{3}$ at impact energies between 100 eV and 1600 eV and scattering angles between 0$^{o}$ and 6$^{o}$ using the translational energy-gain spectroscopy (TES) technique. As apparent from the translational energy-gain measurements, single-electron capture (SEC) from O$_{2}$ and H$_{2}$O proceeds by both dissociative and non-dissociative channels, whereas for N$_{2 }$and CO$_{2}$ only dissociative SEC has been observed. However, for NH$_{3 } $the non-dissociative SEC channel is found to be predominantly populated. Total cross sections have also been compared with available measurements and theoretical calculations based on Landua-Zener model and Demkov model.