I'm looking for information about absorption of light per unit (atom, molecule, stoichiometric) in a liquid vs solid. For instance, imagine a unit cube filled with a saturated solution of, say, potassium permanganate, and shine a laser beam through it from bottom to top and measure the attenuation. Then, evaporate the water and form a single crystal of p.p. in the bottom of the cube, and measure the attenuation of the beam again. In both cases the laser beam passes through the same number of the relevant atoms or molecules. Is there any way to reason whether a given substance will have less, the same, or more attenuation between the liquid form and solid form? It is easy to find data on the different index of refraction between liquids and solids, but are there books or internet resources that make it easy to find optical absorption for various liquid/solid or solution/solid forms of various crystals? Thanks in advance, of course.