Tetraoxygen

Additional recommended knowledge Recognize and detect the effects of electrostatic charges on your balance What is the Correct Way to Check Repeatability in Balances? Safe Weighing Range Ensures Accurate Results Contents 1 Red oxygen 2 Free molecule 3 See also 4 References

O4 is also a subclass of O-class stars.

The tetraoxygen molecule (O₄) was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxygen to obey Curie's law.^[1] Today it seems Lewis was off, but not by far: computer simulations indicate that although there are no stable O₄ molecules in liquid oxygen, O₂ molecules do tend to associate in pairs with antiparallel spins, forming transient O₄ units.^[2] True O₄ does exist, however, as a stable red solid at pressures above 10 GPa.^[3] This phase is known as ε oxygen or red oxygen. Tetraoxygen has also been detected as a short-lived chemical species in mass spectrometry experiments.^[4]

Red oxygen

As the pressure of oxygen at room temperature is increased through 10 GPa, it undergoes a dramatic phase transition to a different allotrope. Its volume decreases significantly,^[5] and it changes color from blue to deep red.^[6] Based on its infrared absorption spectrum, this phase is believed to consist of O₄ molecules in a crystal lattice.^[3]

Liquid oxygen is already used as a rocket fuel, and it has been speculated that red oxygen could make an even better fuel, because of its higher energy density.^[7]

At 96 GPa, oxygen undergoes another phase transition and becomes metallic.^[5]

Free molecule

Theoretical calculations have predicted the existence of metastable O₄ molecules with two different shapes: a "puckered" square like cyclobutane,^[8] and a "pinwheel" with three oxygen atoms surrounding a central one.^[9]

In 2001, a team at the University of Rome La Sapienza conducted a neutralization-reionization mass spectrometry experiment to investigate the structure of free O₄ molecules.^[4] Their results did not agree with either of the two proposed molecular structures, but they did agree with a complex between two O₂ molecules, one in the ground state and the other in a specific excited state.

See also

• Ozone (O₃)
• Tetranitrogen (N₄)

References