Mutual Neutralization in Li⁺−D⁻ Collisions: A Combined Experimental and Theoretical Study

Abstract

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.

Cryogenic merged-ion-beam experiments in DESIREE: Final-state-resolved mutual neutralization of Li+ and D−

“…Here, we present results at 78 ± 13 meV and higher collision energies and compare the present branching fractions with those reported in Ref. [32]. The present experiment confirms the results of that study.…”

“…, are summarized in Fig. 7 and include the results of Launoy et al [32]. Combining the results using the two different techniques suggests that the branching fraction varies little in the energy region below about 1 eV.…”

“…It is also important to study the process at lower center-of-mass energies, closer to the astrophysically relevant energy scale below 1 eV. Recently, in a single-pass experiment, Launoy et al [32] measured final-state-resolved MN of Li + and D − for center-of-mass energies down to 3.9 meV where the 3s, 3p, and 3d states were resolved. Here, we present results at 78 ± 13 meV and higher collision energies and compare the present branching fractions with those reported in Ref.…”

“…We measure the kinetic-energy-release distribution for the mutual neutralization (MN) reactions, which reveals the final quantum-state distributions of the Li and D neutral products. Depending on the internal quantum level schemes, chargeexchange experiments may sometimes be performed with pure ground-state ion beams for atomic ions even at room temperature [32]. This is virtually impossible for studies of collisions involving molecular or cluster ions.…”

Mutual neutralisation of O+ with O−: investigation of the role of metastable ions in a combined experimental and theoretical study

“…11 However, considerable progress has been made in the ability to perform merged-beams measurements under controlled conditions. Recent developments in a merged-beams apparatus in Louvain-la-Neuve have made it possible to fully resolve the final-state distributions of MN reactions, 1,14 with results more consistent with the most recent theory. 12,13 In addition to merged-beams experiments, other apparatuses are also used to study MN, e.g.…”