Charge exchange cross-sections as a function of energy per nucleon for protons (left panel), He⁺-ions, and α-particles (right panel) of the solar wind with interstellar helium and hydrogen. In the upper part of the two panels we show the cross-sections, while the lower parts show the ratio to σ_cx(H⁺ + H → H + H⁺). The black curve in the panels is the reaction H + H⁺ → H⁺ + H. As can be seen in the lower panel the reactions He⁺ + He, He²⁺ + He, and He²⁺ + He⁺ have similar cross-sections as that of H + H⁺ and thus are important in modeling the dynamics of the large-scale astrospheric structures. Note the different y-axis scales between different panels.