Tuesday, 15 September 2009

Colors from vibrations

The inviting blue of a mountain lake or a sea is unique in nature, in that it is caused by vibrational transitions involving hydrogen bonding.

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Blue water is the only known example of a natural color caused by vibrational transitions. In most other cases, color is caused by the interaction of photons of light with electrons. Some of these mechanisms are resonant interactions, such as absorption, emission, and selective reflection. Others are non-resonant, including Rayleigh scattering, interference, diffraction, and refraction. Unlike with water, these mechanisms rely primarily on the interaction of photons with electrons.


Molecular vibrations also have overtones related to their fundamental wavelength. Just as we hear a musical note that is a combination of a fundamental note with its overtones, so molecules may vibrate in complex combinations of their fundamental and overtone vibrations. In water molecules, only the first few overtones make a significant contribution to the overall vibrational energy.




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