Collisional rates for the deactivation of the v₃ state, k_4g,c or k_g,d (solid curves), and for the relaxation of the v₄ state, k_vt (dashed curves). The rates measured in the laboratory by Menard-Bourcin et al. (2005) are shown with solid circles and triangles, in black, with their respective errors. The rates derived in Drossart et al. (1999) are shown with green curves. The k_vt rate measured by Hess & Moore (1976) (blue open diamond) was used in Kim et al. (2014) with a -dependence and is indicated by the blue curve. The upper limit of the k_g rate used by Kim et al. (2014) to derive their lower limit model D for the CH₄ abundance is represented with a filled downward triangle in blue. The rates derived in this work are shown in red.