What is the color of oxygen gas?

[paragchitnis]

The liquid oxygen is blue in color because of unpaired electron in it. (According to molecular orbital theory) In gaseous state also it has unpaired electron but it is colorless gas. Why?
Why color appear due to presence of unpaired electron?

 

[espen180]

The colour appears because of a minute concentration of ozone, according to what I heard. The unpaired electron is responsible for the magnetic properties of the liquid.

 

[paragchitnis]

Why does the blue colour appear due to minute presence of ozone? I have heard only about unpaired electronic arrangement as the reason of the presence of colour. My concept may be wrong! Will you explain?

 

[espen180]

It may also be due to exitation of the oxygen molecules by photons. Red, yellow ang green peaks in the absorption spectrum could give rise to the blue colour. The colour dissapears when the liquid is passed through activated silica gel, so there might be some kind of equilibrium. Remember that in a liquid, the molecules are much closer than in a gas, so the stronger interaction might produce effects not present in the gaseous phase.

Whether this is accurate or not is beyond my knowledge.

 

[paragchitnis]

It may be correct. But I am unable to find out the relation between pairing of electrons and the colour of the compound

 

[espen180]

It might be related to how O₂ molecules form weakly bonded molecule pairs whose spins, and therefore magnetic moments, are antiparallel.