[5] Theoretical calculations have predicted the existence of metastable O4 molecules with two different shapes: a "puckered" square like cyclobutane or S4,[6] and a "pinwheel" with three oxygen atoms surrounding a central one in a trigonal planar formation similar to boron trifluoride or sulfur trioxide.
[7][8] It was previously pointed out that the "pinwheel" O4 molecule should be the natural continuation of the isoelectronic series BO3−3, CO2−3, NO−3,[9] and analogous to SO3; that observation served as the basis for the mentioned theoretical calculations.
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.
[10] Though it's use is highly speculative due its unstable nature, it has been theorized that tetraoxygen could be an alternative to traditional liquid oxygen in rocket propulsion.
Its higher density—approximately twice that of liquid oxygen—could allow for smaller oxidizer tanks, reducing overall vehicle mass and potentially increasing payload capacity.