Red oxygen

Red oxygen, or tetraoxygen (O₄) is an allotrope of oxygen occuring in extremely high pressures (in order of 20 GPa). Under such pressures the normally blue solid oxygen turns deep red, together with great reduction of its volume. Its absorption spectrum suggests the formation of O₄ molecules. It is much more powerful oxidizer than oxygen or ozone, and its properties are being studied for use in rocket fuels and other applications.

With further pressure increase, at 96 GPa oxygen becomes metallic.

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