Energy levels, transition frequencies and Einstein A coefficients were taken from CDMS version 4 of May 2007. Collisional rate coefficients are from Dumouchel et al (2010) who have also made calculations for HNC. The set of rate coefficients was scaled by a factor 1.37 to represent collisions with H₂. Electron collision rates are taken from Faure et al (2007) and cover the levels up to J=8 for temperatures from 5 to 800 K.

We also provide older collisional calculations from Green & Thaddeus (1974) and Green (unpublished data), extrapolated for the temperature range from 5 to 1200 K, and including energy levels up to J=29. for collisions with He. This dataset may still be useful to model high-J line observations of HCN. For details on the extrapolation see Schöier et al. (2005).

The third datafile takes the hyperfine splitting (hfs) of the levels up to J=8 into account. Collision data with H₂ for temperatures from 5 to 30 K are taken from Hernandez Vera et al (2017). For a discussion of various calculations of HCN hyperfine collision rates please see Braine et al (in prep.)