Re: Color of oxygen

On Mar 21, 3:58 pm, tadchem <tadc...@xxxxxxxxxxx> wrote:
On Mar 21, 2:17 pm, mike3 <mike4...@xxxxxxxxx> wrote:



On Mar 21, 10:51 am, tadchem <tadc...@xxxxxxxxxxx> wrote:

On Mar 20, 7:20 pm, mike3 <mike4...@xxxxxxxxx> wrote:

Hi.

Why is it that liquid oxygen has a bluish color, but as a gas it has
no color at all? (at least not to any visible degree.) Is it just
because the gas is of a low density, or something else?

How much detail can you handle?http://www.rsbs.anu.edu.au/O2/O2_1_%20ElectronicConfig.htm

So then the gas has a different emission/absorption profile than
the liquid, which does not include the sharp peaks in the
visible, hence it appears colorless.

Is this right?

Yes. In the liquid, the close proximity of other molecules to the
electrons of any given molecule is enough to alter the electronic
energy states in the molecule of interest. Usually this shifts the
main spectral bands to lower energies. Oxygen gas absorbs a lot in
the UV - that's one of the mechanisms for formation of the ozone
layer, and why oxygen and ozone in the stratosphere protect us from
hard UV rays. Condensing the gas to a liquid shifts some of these
absorption bands into the visible range, resulting in color.

Water is the same way. Water vapor is colorless, but large quantities
of the liquid are a bluish-green (or greenish-blue, if you prefer).
The absorbtion bands of liquid water are very weak, but they do occur
in the visible range, absorbing preferentially red (and infrared)
light.


Hmm. I thought it was just because the water has hardly any color
anyway,
so if you need huge quantities of liquid you'd need even huger
quantities of
gas, but I guess the gas would still be colorless no matter how much
you looked
through since the electron dynamics is different (although effects
like Rayleigh
scattering may give it "non-intrinsic" color eventually, like how the
sky is
made blue even though all the gases in there are 100% colorless (i.e.
no
"intrinsic" color)).

I'm curious, are there any gases that _do_ have visible color? (gases
in
general, not necessarily _elements_.)
.

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