Elastic and exchanged atom–molecule collisions in ⁴He–⁴He–X (X = ⁴⁰K, ⁸⁵Rb, ¹³³Cs) systems at low energy.

This article focuses on the low-energy three-body collision properties of systems composed of two helium-4 (^4He) atoms and one alkali-metal atom X (X = ^40K, ^85Rb, ^133Cs). Using the adiabatic hyperspherical representation combined with the R-matrix propagation method, the study solves the three-body Schrödinger equation with realistic pairwise potentials to calculate atom–dimer scattering lengths, elastic and inelastic atom–molecule cross sections, collision exchange rates, and three-body recombination rates. Results reveal that elastic cross sections at low energies can be approximated by four times pi times the square of the atom–dimer scattering length, and that inelastic cross sections for the exchange process ^4He_2 + X → ^4HeX + ^4He exhibit universal behavior when scaled by the two-body ^4HeX scattering lengths. These findings enhance understanding of universal quantum few-body effects in weakly bound helium–alkali-metal systems relevant to ultracold atomic and molecular physics.