Cross sections for positron scattering from ethane

Abstract

We report experimental and theoretical cross sections for positron scattering from the fundamental organic-chemistry molecule ethane (C${}_{2}$H${}_{6}$). The experimental total cross sections (TCSs) were obtained using a linear transmission technique, for energies in the range 0.1--70 eV and with an energy resolution of $\ensuremath{\sim}$0.25 eV (full width at half maximum). Agreement, over the common energy range, with the earlier TCS measurements of Floeder et al. [J. Phys. B 18, 3347 (1985)] is excellent, while both the present results and those of Floeder et al. are consistently higher in magnitude than the data of Sueoka and Mori [J. Phys. B 19, 4035 (1986)]. The present calculations employed the Schwinger multichannel method and were performed in the static plus polarization approximation for energies up to 10 eV. Our calculated elastic integral cross sections (ICSs) indicate a Ramsauer-Townsend minimum at around 1.4 eV in the ${A}_{g}$ scattering symmetry, and a virtual state. In addition we calculated from our scattering cross section a scattering length of $\ensuremath{-}$13.83${a}_{0}$. Agreement between our measured TCS and calculated elastic ICS is found to be only qualitative, although this is perhaps not so surprising given the TCS below 10 eV in principle includes contributions from rotational, vibrational, and electronic-state excitation and positronium formation whereas the calculation does not.