Rates for the de-excitation of C₂H through collision with H₂ at 100 K. Black crosses mark all collision rates from Spielfiedel et al. (2012) above 10^-12 cm³s^-1. The curves indicate the different transition series for pure rotational transitions of the molecule, i.e., ΔN = ΔJ = ΔF. Each series consists of four curves according to the fine and hyperfine structure split of the four N states with approximately the same energy: J = N ± /1/2 and F = J ± 1/2. The continuations of those curves into the colored symbols show the extrapolation of the rates to the higher level transitions using the formalism from Schöier et al. (2005) based on the IOS approximation.