Cryogenic merged-ion-beam experiments in DESIREE: Final-state-resolved mutual neutralization of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>Li</mml:mi></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi mathvariant="normal">D</mml:mi></mml:mrow><mml:mo>−</mml:mo></mml:msup></mml:math>
Gustav Eklund, Jon Grumer, Stefan Rosén, MingChao Ji, Najeeb Punnakayathil, A. Källberg, A. Simonsson, Richard Thomas, Mark H. Stockett, P. Reinhed, P. Löfgren, M. Björkhage, Mikael Blom, P. S. Barklem, H. Cederquist, Henning Zettergren, H. T. Schmidt
Abstract
We have developed an experimental technique to study charge- and energy-flow processes in sub-eV collisions between oppositely charged, internally cold, ions of atoms, molecules, and clusters. Two ion beams are stored in separate rings of the cryogenic ion-beam storage facility DESIREE, and merged in a common straight section where a set of biased drift tubes is used to control the center-of-mass collision energy locally in fine steps. Here, we present measurements on mutual neutralization between ${\mathrm{Li}}^{+}$ and ${\mathrm{D}}^{\ensuremath{-}}$ where a time-sensitive imaging-detector system is used to measure the three-dimensional distance between the neutral Li and D atoms as they reach the detector. This scheme allows for direct measurements of kinetic-energy releases, and here it reveals separate populations of the $3s$ state and the $(3p+3d)$ states in neutral Li while the D atom is left in its ground state $1s$. The branching fraction of the $3s$ final state is measured to be $57.8\ifmmode\pm\else\textpm\fi{}0.7%$ at a center-of-mass collision energy of $78\ifmmode\pm\else\textpm\fi{}13$ meV. The technique paves the way for studies of charge-, energy-, and mass-transfer reactions in single collisions involving molecular and cluster ions in well-defined quantum states.