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If you look online you can find various graphs of the absorption spectrum of water. The graph below for examples comes from this blog post.

absorption spectrum of light

As far as I can tell these graphs come from empirical measurements. Is there a theoretical model that can derive the same or similar results? Of course if it was easy to implement in software that would be ideal.

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  • $\begingroup$ You can for examble retrieve line date for a number of different molecules to build up absorption spectra from the HITRAN data base. In the corresponding papers, they also give references and explanations how these parameters are calculated. $\endgroup$ – Nemo Jun 9 '13 at 19:34
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The easy answer is no. It is possible to calculate absorption spectra from molecular structures using quantum mechanical calculation programs (for instance DFT using Gaussian) starting from the Schrödinger equation. These programs only work for a relatively small number of electrons though and therefore usually assume gas phase including a small correction for the surroundings. Liquid phase water, where the molecules are very strongly coupled will be extremely difficult to calculate since it is almost impossible to create a "box" of relevant molecules. I don't have SciFinder or something equivalent, but a search on Google only gave articles calculating X-ray spectra.

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