  We present a combined experimental and theoretical study of the mutual
neutralization process in collisions of lithium ions (Li+) with deuterium
anions (D-) at collision energies below 1 eV. We employ a merged-beam apparatus
to determine total and state-to-state mutual neutralization cross sections. We
perform nuclear dynamics calculations using the multi-channel Landau-Zener
model based on accurate ab initio molecular data. We obtain an excellent
agreement between the experimental and theoretical results over the energy
range covered in this work. We show that the basis sets used in the ab initio
calculations have a limited influence on the total cross section, but strongly
impacts the results obtained for the partial cross sections or the reaction
branching ratios. This demonstrates the important role of high-precision
measurements to validate the theoretical approaches used to study gas-phase
reactive processes. Finally, we compute mutual neutralization rate coefficients
for Li+ + H- and Li+ + D-, and discuss their significance for astrochemistry
models.
