State Selective Scattering Angle Dependent Capture Cross Sections Measured by Cold Target Recoil Ion Momentum Spectroscopy

Abstract

We have developed a new kind of recoil ion momentum spectroscopy technique, using a precooled supersonic gas jet target, to determine state selective, scattering angle dependent cross sections for swift ion-atom collisions ( $0.25,\dots{},1\mathrm{MeV}{\mathrm{He}}^{2+}$ on He), by measuring the transverse and longitudinal momentum of the recoil ion. A longitudinal momentum resolution of $\ifmmode\pm\else\textpm\fi{}0.13\mathrm{a}.\mathrm{u}.$ was achieved, about a factor of 30 better than ever obtained before, which enables a clear separation of K and L shell capture. In the transverse direction a resolution corresponding to a projectile scattering angle uncertainty of $\ensuremath{\Delta}{\ensuremath{\vartheta}}_{P}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}1\ensuremath{\mu}\mathrm{rad}$ was obtained.