Single-electron capture processes in slow collisions ofHe2+ions withO2,NH3,N2, andCO2

Abstract

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture (SEC) in collisions of ${\mathrm{He}}^{2+}$ ions with ${\mathrm{O}}_{2}$, $\mathrm{N}{\mathrm{H}}_{3}$, ${\mathrm{N}}_{2}$, and $\mathrm{C}{\mathrm{O}}_{2}$ at laboratory impact energies between 25 and $400\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{amu}$. The measured spectra for the ${\mathrm{He}}^{2+}\ensuremath{-}{\mathrm{N}}_{2}$ and $\mathrm{C}{\mathrm{O}}_{2}$ collision systems show that the dominant reaction channel is due to dissociative transfer ionization (i.e., SEC accompanied by ionization of the molecular target ion). In the case of the ${\mathrm{He}}^{2+}\ensuremath{-}\mathrm{N}{\mathrm{H}}_{3}$ collision system, nondissociative single-electron capture into $n=2$ states of ${\mathrm{He}}^{+}$ with production of $\mathrm{N}\mathrm{H}_{3}{}^{+}$ in the ground state is predominantly populated. These processes are observed to be the dominant reaction channels over the entire impact energy region studied and at laboratory scattering angles between 0\ifmmode^\circ\else\textdegree\fi{} and 8\ifmmode^\circ\else\textdegree\fi{}. The energy dependence of total cross sections for SEC are also measured and found to slowly increase with increasing impact energies. The measured cross sections are also compared with the available measurements and theoretical results based on the Demkov and Landau-Zener models.