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Physical Review A

Final-state-resolved mutual neutralization of Na+ and D−

Gustav Eklund, Jon Grumer, P. S. Barklem, Stefan Rosén, MingChao Ji, A. Simonsson, Richard Thomas, H. Cederquist, Henning Zettergren, Henning T. Schmidt

Published Mar 12, 2021• 17 citations
Publisher

Abstract

The present paper reports on a merged-beam experiment on mutual neutralization between ${\mathrm{Na}}^{+}$ and ${\mathrm{D}}^{\ensuremath{-}}$. For this experiment, we have used the DESIREE ion-beams storage-ring facility. The reaction products are detected using a position- and time-sensitive detector, which ideally allows for determination of the population of each individual quantum state in the final atomic systems. Here, the $4s, 3d$, and $4p$ final states in Na are observed and in all cases the D atom is in its ground state $1s ^{2}S$. The respective branching fractions of the states populated in Na are determined by fitting results from a Monte Carlo simulation of the experiment to the measured data. The center-of-mass collision energy is controlled using a set of biased drift tubes, and the branching fractions are measured for energies between 80 meV and 393 meV. The resulting branching fractions are found to agree qualitatively with the only available theoretical calculations for this particular system, which are based on a multichannel Landau-Zener approach using dynamic couplings determined with a linear combination of atomic orbitals model.

DOI
10.1103/physreva.103.032814

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The present paper reports on a merged-beam experiment on mutual neutralization between Na+{\mathrm{Na}}^{+}Na+ and D\ensuremath−{\mathrm{D}}^{\ensuremath{-}}D\ensuremath−. For this experiment, we have used the DESIREE ion-beams storage-ring facility. The reaction products are detected using a position- and time-sensitive detector, which ideally allows for determination of the population of each individual quantum state in the final atomic systems. Here, the 4s,3d4s, 3d4s,3d, and 4p4p4p final states in Na are observed and in all cases the D atom is in its ground state 1s2S1s ^{2}S1s2S. The respective branching fractions of the states populated in Na are determined by fitting results from a Monte Carlo simulation of the experiment to the measured data. The center-of-mass collision energy is controlled using a set of biased drift tubes, and the branching fractions are measured for energies between 80 meV and 393 meV. The resulting branching fractions are found to agree qualitatively with the only available theoretical calculations for this particular system, which are based on a multichannel Landau-Zener approach using dynamic couplings determined with a linear combination of atomic orbitals model.
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 Li+{\mathrm{Li}}^{+}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 3s3s3s state and the (3p+3d)(3p+3d)(3p+3d) states in neutral Li while the D atom is left in its ground state 1s1s1s. The branching fraction of the 3s3s3s 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.
We have studied low-energy mutual neutralization in reactions of Si − with Na + and with K + ions at the merged-beam double ion-beam storage-ring facility DESIREE. We made measurements with and without a significant fraction of the Si − ions in the metastable D 2 level. The latter was achieved by state-selective photodetachment. The data reveal contributions from spin-forbidden mutual-neutralization reactions, i.e., violations of Wigner's spin-conservation rule. For the Na + + Si − case, the dominating such reaction channel is obscured when metastable Si − ions are present in the beam.
We report on mutual neutralization measurements between 7Li+^{7}\mathrm{Li}^{+}7Li+ and $^{1}\mathrm{H}^{\ensuremath{-}}$ at effective center-of-mass collision energies in the range of 100 to 350 meV. We find that final states of lithium with principal quantum number n=3n=3n=3 dominate with 3s3s3s separated from the unresolved 3p3p3p and 3d3d3d states. We measure the 3s3s3s branching fraction to be 0.665(12) at 100(16) meV and no significant dependence on collision energy is observed in the studied range. Comparing to previous results on mutual neutralization between 7Li+^{7}\mathrm{Li}^{+}7Li+ and $^{2}\mathrm{H}^{\ensuremath{-}}$ [G. Eklund et al., Phys. Rev. A 102, 012823 (2020)], we find that 7Li+^{7}\mathrm{Li}^{+}7Li+ collisions with $^{1}\mathrm{H}^{\ensuremath{-}}$ result in a significantly higher 3s3s3s branching fraction than collisions with $^{2}\mathrm{H}^{\ensuremath{-}}$. The difference is 0.087(14). The 3s3s3s branching fraction of $^{7}\mathrm{Li}^{+} + ^{1}\mathrm{H}^{\ensuremath{-}}$ and the determined isotope difference are in agreement with results from extended full quantum calculations based on the same input data and numerical method as in Croft et al. [H. Croft, A. S. Dickinson, and F. X. Gad\'ea, J. Phys. B 32, 81 (1999)]. These calculations reveal strong Stueckelberg oscillations of the 3s3s3s branching fraction for both isotopes.
A summary of research performed under AFOSR Grant No. 83-0242 is given. The review describes molecular-beam studies of ion-pair production and measurements of the fraction of excited Na atoms, F*, in a composite beam of ground-state and excited Na atoms. Molecular beam techniques will be employed to study two-body reactions that will result in an intense, collimated beam of Li atoms at an energy of several hundred keV. Generating such a beam by charge transfer of a Li/sup +/ beam is not efficient at this energy. It appears that it can most efficiently be produced by forming a Li/sup -/ beam and stripping away valence electrons in a suitable gas. Plans are to study reactions associated with the production of Li/sup -/ beam which is formed when a Li/sup +/ beam interacts with a vapor of ground and excited (resonance state) Na atoms. One of the reactions (after Li/sup +/ has been converted to Li) is Li + Na yield Li/sup -/ + Na(+). This will be examined by merging a Li beam with a beam of Na atoms excited with a single frequency dye laser. The instrumentation required to complete this study consists of some laser and optical components,more » some vacuum equipment, and a laboratory computer system for data acquisition and analysis. This apparatus will supplement as well as rejuvenate an existing merging-beam apparatus.« less
A combined optical-pumping--laser-induced-fluorescence method was developed to determine the fraction of metastable-state ions in a Ba+{\mathrm{Ba}}^{+}Ba+ beam. This allowed us to measure the ratio of the charge-exchange cross sections for collisions of Ba+{\mathrm{Ba}}^{+}Ba+(6s) and Ba+{\mathrm{Ba}}^{+}Ba+(5d) ions with a sodium vapor for impact energies ranging from 3 to 29 keV. For a collision energy of 5 keV, the ratio of the cross sections for Ba+{\mathrm{Ba}}^{+}Ba+(5d 2^{2}2D3/2{\mathit{D}}_{3/2}D3/2​) and Ba+{\mathrm{Ba}}^{+}Ba+(5d 2^{2}2D5/2{\mathit{D}}_{5/2}D5/2​) was measured. All results are compared to theoretical near-resonance predictions.
We present measurements of the charge-exchange reaction rate between neutral sodium (Na) and ionized calcium (Ca+{\mathrm{Ca}}^{+}Ca+) in a hybrid atom-ion trap, which is comprised of a Na magneto-optical trap concentric with a linear Paul trap. Once the Na and Ca+{\mathrm{Ca}}^{+}Ca+ are co-trapped, the reaction rate is measured by continuously quenching the reaction product Na+{\mathrm{Na}}^{+}Na+ from the ion trap, and then destructively measuring the decay of the remaining ion population. The reactants' electronic state and temperature are experimentally controlled, allowing us to determine the four individual reaction rates between Na[SorP]\text{Na}[S\phantom{\rule{4.pt}{0ex}}\text{or}\phantom{\rule{4.pt}{0ex}}P]Na[SorP] and Ca+[SorD]{\text{Ca}}^{+}[S\phantom{\rule{4.pt}{0ex}}\text{or}\phantom{\rule{4.pt}{0ex}}D]Ca+[SorD] at different collision energies. With the exception of the largest reaction-rate channel (Na[P]+Ca+[D]\text{Na}[P]+{\text{Ca}}^{+}[D]Na[P]+Ca+[D]), our rates are consistent with the classical Langevin rate limit. We have also found evidence of reactant collision-energy thresholds associated with two of the four entrance channels.