Angular distribution of low-energy electron emission in collisions of 6-MeV/u bare carbon ions with molecular hydrogen: Two-center mechanism and interference effect

Abstract

We report the energy and angular distribution of electron double differential cross sections (DDCS) in collision of $6\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}\phantom{\rule{0.3em}{0ex}}{\mathrm{C}}^{6+}$ ions with molecular hydrogen. We explain the observed distributions in terms of the two-center effect and the Young-type interference effect. The secondary electrons having energies between 1 and $1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ are detected at about 10 different emission angles between $30\ifmmode^\circ\else\textdegree\fi{}$ and $150\ifmmode^\circ\else\textdegree\fi{}$. The measured data are compared with the state-of-the-art continuum distorted wave-eikonal initial state and the first Born model calculations which use molecular wave function. The single differential cross sections are derived and compared with the theoretical predictions. The oscillations due to the interference effect are derived in the DDCS ratios using theoretical cross sections for the atomic H target. The effect of the atomic parameters on the observed oscillations is discussed. An evidence of interference effect has also been shown in the single differential cross section. The electron energy dependence of the forward-backward asymmetry parameter shows a monotonically increasing behavior for an atomic target, such as He, which could be explained in terms of the two-center effect only. In contrast, for the molecular ${\mathrm{H}}_{2}$ the asymmetry parameter reveals an oscillatory behavior due to the Young-type interference effect superimposed with the two-center effect. The asymmetry parameter technique provides a self-normalized method to reveal the interference oscillation which does not require either a theoretical model or complementary measurements on the atomic H target.