Energy levels, transition frequencies and Einstein A coefficients were taken from the CDMS catalog (Müller et al 2005). Collisional rate coefficients with H₂ are from Spielfiedel et al (2012), scaled by 1.36 from their rates with He. The original calculations cover energy levels up to 105 cm^-1 and temperatures up to 100 K; here we provide extrapolations to 445 cm^-1 and 250 K. Electron impact rates were calculated in the Born approximation by Alex Faure for temperatures from 10 to 1000 K and covering energy levels up to 945 cm^-1 above ground. For a detailed description of the collision data see Nagy et al (2015).

Data with ortho and para H₂ as separate collision partners were calculated by Dagdigian (2018). These data also resolve the hyperfine structure of C₂H. This second datafile does not include electron collisions.