Energy loss function for protons colliding with H₂ (solid black line). Coloured lines show the different components and the following references point to the papers from which the relative cross sections have been adopted: momentum transfer (‘m.t.’, solid blue; Pinto & Galli 2008); the rotational transition J = 0 → 2 (solid green line; Gianturco & Tritella 1977; Linder 1980); vibrational transitions v = 0 → 1 and v = 0 → 2 (solid and dashed red lines, respectively; Gentry & Giese 1975; Herrero & Doering 1972; Schinke 1977; Niedner et al. 1987; Janev et al. 2003); dissociation (solid orange line; Janev et al. 2003); Lyα (solid pink line; van Zyl et al. 1967, 1989; Phelps 1990); Hα (solid brown line; Williams et al. 1982); electron capture (solid purple line; Gilbody & Hasted 1957; Curran et al. 1959; De Heer et al. 1966; Toburen & Wilson 1972; Rudd et al. 1983; Gealy & van Zyl 1987; Baer et al. 1988; Phelps 1990; Errea et al. 2010); ionisation (solid cyan line; Rudd 1988; Krause et al. 2015); and pion production (solid yellow line; Krakau & Schlickeiser 2015). Dash-dotted grey lines show the Coulomb losses at 10 K for an ionisation fraction of 10⁻⁷ (Mannheim & Schlickeiser 1994).