Top panel: Cross sections for collisions of C⁺ with H vs. collision energy in the center-of-mass frame E_cm: m.t. cross section computed by Flower & Pineau des Forets (1995) (filled triangles), fit from Pinto & Galli (2008) (solid line), and Langevin m.t. cross section (dashed line). Experimental data for the c.e. cross section: Phaneuf et al. (1978) (empty circles), Goffe et al. (1979) (empty squares), and Stancil et al. (1998) (filled triangles), and c.e. cross section recommended by Stancil et al. (1998) (solid line). Bottom panel: Collisional rate coefficients: Langevin m.t. (dashed line), and m.t. and c.e. (solid lines).