Collisional rate coefficients are taken from the literature and include collisions with: H (Launay and Roueff 1977), e (Johnson et al. 1987), H⁺ (Roueff & Le Bourlot 1990), He (Stämmler & Flower 1991), and H₂ (Schröder et al. 1991).
More recent calculations for C-H collisions by Abrahamsson et al (2007) exist, but the difference with the Launay & Roueff rates is small.