Do you know where I can find a library with absorption spectra? I would like it if then I could input a wavelength and get back a specific value. More specifically I would like to see the absorption spectra of different components in tissue.
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There are lots of emission and absorption lines – at different energy scales. Atomic spectra, vibrational spectra, rotational spectra, and so on.
For each of them, one may discuss millions of molecules in principle (most of the large number are organic molecules). The amount of data to cover "everything" is clearly unrealistically huge. But any subset of such tasks has tables that are useful. For example, a 160-page-long text of molecular vibrational frequencies is here:
The molecules must be well-defined. "Tissues" in the sense of biology contain lots of materials that are very complex and non-unique. Each person has a different DNA, except for twins, maybe. People really have inequivalent proteins, too. And the number of lines etc. is so complex – and dependent on the orientation of these molecules – that it becomes meaningless to describe the spectra "rigorously".