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

We investigate the low-energy collision properties of the 4He-4He-X (X = 40K, 85Rb, 133Cs) systems using the R-matrix propagation method within the hyperspherical coordinate framework. The atom-dimer scattering length and atom-molecule collisional exchange rates are derived by solving the three-body Schrödinger equation using a potential energy surface obtained by summing three realistic pairwise potentials. Our results show that the atom-molecule collision exchange rates in the 4He2 + X → 4HeX + 4He process are primarily governed by the 4HeX two-body scattering lengths. Furthermore, when scaled by this parameter, the inelastic cross sections for all three systems collapse onto a single curve, demonstrating universal behavior. These findings provide new insights into the fundamental properties of weakly bound helium-helium-alkali-metal systems and their role in low-energy three-body collisions.