Top panel: Cross sections for collisions of H⁺ with He vs. collision energy in the center-of-mass frame E_cm. Momentum transfer cross section from Krstić & Schultz (1999, 2006), Langevin m.t. cross section (dashed line), charge exchange cross section from Loreau et al. (2018), and and ionization cross section from Shah & Gilbody (1985). Experimental data for the c.e. cross section: Martin et al. (1981) (empty triangles), Shah & Gilbody (1985) (filled triangles), Shah et al. (1989) (empty squares), and Kusakabe et al. (2011) (filled squares). Experimental data for the ionization cross section: Shah & Gilbody (1985) (empty circles). Bottom panel: Collisional rate coefficient for Langevin m.t. (dashed line), and for m.t. and c.e. (solid lines).