Water is intrinsically blue because of molecular vibrations. The topic is covered here: Only sea water appears blue in color, why this is not happening in river water?

And here, which I post because it also includes why heavy water is not blue.

water absorbtion http://www.dartmouth.edu/~etrnsfer/water.htm

I have read that ice is less blue and more turquoise, from which I take that on freezing the absorption spectrum is shifted slightly towards longer wavelengths and lets thru more green - like deuterium but to a lesser degree.

The questions:

1: would heating (liquid) water shift the absorption spectrum towards shorter wavelengths and make water appear more violet? As it gets hotter and hotter (but pressure compels it to stay liquid) would the apparent color move more and more from blue to violet?

2: Would light water made with the isotope O15 appear more violet for the same reason heavy water has no color?

  • $\begingroup$ I am not sure of a correct answer: but my guess is it would actually shift the other way - toward the red , at least for the molecular vibrations, because more heat effectively stretches the bonds. Stretched bonds will have a longer frequency due to the anharmonicity that at high enough energies ultimately culminates in bond breakage. As I said, just a guess - could be 100% wrong, so I'm not posting this as an answer. $\endgroup$ – The_Sympathizer Apr 21 '19 at 5:59
  • $\begingroup$ @The_Sympathizer - well if freezing it stretches a little towards the red, and more massive water stretches a lot toward the red, I thought maybe heat would stretch towards the blue. $\endgroup$ – Willk Apr 21 '19 at 20:20
  • $\begingroup$ Is complicated because in water hydrogen bonds are so important that an internal molecular analysis won't suffice. The vibrations that appear as harmonics in Vis are strongly influenced by this. Nice question, at least in principle. Note that perhaps phenomena others than absorption might dictate what we see (scattering for instance, in ice). $\endgroup$ – Alchimista Apr 22 '19 at 7:44

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