Energy loss function for electrons 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; England et al. 1988); vibrational transitions v = 0 → 1 (solid red line; Yoon et al. 2008) and v = 0 → 2 (dashed red line; Janev et al. 2003); electronic transitions summed over all the triplet and singlet states (solid orange and magenta lines, respectively; Scarlett et al. 2021); Lyman series (solid pink lines; van Zyl et al. 1989; Ajello et al. 1991, 1996); Balmer series (solid brown lines; Möhlmann et al. 1977; Karolis & Harting 1978; Williams et al. 1982); ionisation (solid cyan line; Kim et al. 2000); bremsstrahlung (solid grey line; Blumenthal & Gould 1970; Padovani et al. 2018a); and synchrotron (solid yellow line; Schlickeiser 2002). Dash-dotted grey lines show the Coulomb losses at 10 K for ionisation fractions equal to 10⁻⁷ and 10⁻⁸ (Swartz et al. 1971) and the solid yellow line shows the synchrotron losses (Schlickeiser 2002).