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Journal of Physics B Atomic Molecular and Optical Physics

Elastic and charge-transfer collisions of He + –He at ultralow energies

Syham Lias, Fouzia Bouchelaghem, L. Aissaoui

Published Apr 15, 2026• 1 citation
Publisher

Abstract

Abstract Elastic, momentum-transfer (diffusion), and non-radiative charge-transfer cross sections are calculated for collisions between ground-state He + ( 2 S) ions and neutral He( 1 S) atoms over an energy range spanning fourteen orders of magnitude, from 10 −12 to 1 atomic unit. In this ultralow-energy regime, quantum mechanical effects dominate and the indistinguishability of helium nuclei necessitates a rigorous treatment of exchange symmetry. Phase shifts are computed using highly accurate ab initio potential energy curves for the X 2 Σ u and A 2 Σ g molecular states. The resulting elastic σ el , diffusion σ d , and charge-transfer σ ct cross sections reveal three distinct regimes: at energies below 10 −9 a.u., cross sections exceed 10 5 a 0 2 and are dominated by long-range polarization forces; in the intermediate range (10 −8 –10 −4 a.u.), pronounced quantum interference structures appear; at higher energies, results converge to semiclassical E −1/3 behavior. The data provide benchmark cross sections for ultracold ion–atom collision modeling relevant to cold-ion physics and hybrid atom–ion trapping experiments.

DOI
10.1088/1361-6455/ae6001

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There has been considerable recent interest in low-temperature interrogation of quantum helium nanodroplets. We consider the interaction of helium ground and metastable states, employing the best known molecular dimer potentials. Radiative transitions between different metastable rovibrational levels are compared with the discharge emission transition lines and good agreement is found. Collisional interactions between helium ground and metastable atoms are studied and elastic scattering, metastability excitation transfer and diffusion cross sections and rate coefficients are calculated at ultralow energies. The integral elastic cross section at ultralow energies is about 5000A˚2.5000 {\mathrm{\AA{}}}^{2}.5000A˚2. Effect of shape resonances that form in the potential barriers, on the cross sections is investigated. We find that some shape resonances live for longer than 100 s. Long-range potential wells could support ``shelf'' levels. We discuss their collisional and spectroscopic properties.