*CIA Section

1. .cia files can be downloaded from the HITRAN web-site.

2. If a filename template DEFCIA is supplied, identified by containing a '*' character, first all the explicitly specified files are read, then '*' character in the template is expanded to all possible combinations of the molecules specified in the *GAS section, as well as 'Air'. But if you have both 'Air' and a specific molecule specified as broadening gases for a particular spectral range, the RFM will return a fatal error message (as you would expect).

3. When looking for filenames, molecule names are mixed case, although in practice for most molecules represented by .cia files this is the same as upper case (eg 'H2O', 'CH4'), apart from 'He' and 'Air'.

4. The order of molecules, eg O2-CO2 or CO2-O2, is not significant. Using the wildcard, both combinations are checked.

5. Warning: you may get step-like discontinuities using CIA data. For example the file N2-N2_2021.cia contains spectra 0–450 cm^-1 for temperatures up to 200 K, 0–550 cm^-1 for 210–300 K, and 0–650 cm^-1 for 300–400 K.
   To calculate an absorption spectrum from 0–650 cm^-1 at, say, 185 K, the RFM interpolates the 180 and 190 K spectra up to 450 cm^-1 but beyond that point has to use the coldest available tabulation: 210 K up to 550 cm^-1 and then 210 K up to 650 cm^-1, creating 'steps' in absorption. To avoid this you would need to modify the CIA data file to extrapolate all spectra up to 650 cm^-1.

*CIA ../rfm_files/N2-N2_2011.cia ! CIA data for N2-N2 ../rfm_files/*_2011.cia ! Other data, eg N2-CH4, O2-N2