Exploring Low Energy Molecular Ion Reactions with Merged Beams

Abstract

Charge transfer in molecular ion–neutral interactions can proceed through dynamically coupled electronic, vibrational, and rotational degrees of freedom. Using the upgraded Oak Ridge National Laboratory ion–atom merged–beams apparatus, absolute direct charge transfer is explored from keV/u collision energies where the collision is considered “ro–vibrationally frozen” to sub–eV/u collision energies where collision times are long enough to sample vibrational and rotational modes. Our first molecular ion measurement with the merged-beams apparatus has been performed for D2+ + H and is used to benchmark high energy sudden approximation theory and vibrational specific adiabatic theory for the (H2–H)+ complex. CT measurements have also been performed for D3+ + H from 2 eV/u to 2 keV/u and CO+ + H from 20 eV/u to 2000 eV/u. With straightforward improvements to the apparatus, we plan to extend our measurements to key "destructive" rate coefficients for H2+ and CH+ with H at temperatures relevant to the interstellar medium.