- O4 is also a subclass of O-class stars.
), also called oxozone 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
. 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. In 1999, researchers thought that solid oxygen
existed in its ε-phase (at pressures above 10 GPa
) as O4
. However, in 2006, it was shown by X-ray crystallography
that this stable phase
known as ε oxygen
or red oxygen
is in fact
. Nevertheless, tetraoxygen has been detected as a short-lived chemical species
in mass spectrometry
Theoretical calculations have predicted the existence of metastable O4 molecules with two different shapes: a "puckered" square like cyclobutane, and a "pinwheel" with three oxygen atoms surrounding a central one in a trigonal planar formation similar to Boron Trifloride.
|| D3h structure |
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. 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.