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How to calculate the absorption coefficient (for radiation) from HITEMP or HITRAN databases?

Or where can I find some tables or plots for the absorption coefficient?

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I think you need to be more specific. The absorption cross-sections reported in these databases are determined empirically and vary by temperature and molecule. If you want a plot or table you should mention which molecule, temperature regime, and wavelength region you are interested in. –  farrenthorpe Jul 5 at 13:27
@farrenthorpe I need at least some examples of tables for some temperatures and infrared wavelengths, for example, for air or another gases. –  jokersobak Jul 5 at 22:38
air is a mixture... i wouldn't think "air" is in the Hitran database. there are also different entries depending on the author/researcher. Here check out this link: vpl.astro.washington.edu/spectra/o3.htm –  farrenthorpe Jul 5 at 23:25
Are you talking about the attenuation coefficient, which is in inverse centimeters? Or just the absorption portion (no scattering) of the attenuation? The HITRAN data I pointed to is in square centimeters per molecule which is how absorption is quantified in the lab. I suggest you look at the wikipedia pages en.wikipedia.org/wiki/Electromagnetic_absorption_by_water and en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law ... I've never studied Beer's Lambert law using an "absorption coefficient" but apparently it's just the cross section times number of molecules in the path. –  farrenthorpe Jul 6 at 14:57
The HITRAN "intensity" parameter for each spectral line can be converted into an absorption cross-section as a function of wavelength. (For example code showing how to do this conversion, see github.com/nzhagen/hitran) Using Beer's law you can then take the given cross-section of a gas, select a wavelength, and calculate the absorption for a given gas concentration and path length through the gas. –  nzh Aug 29 at 15:27