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Octaoxygen

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Octaoxygen is an allotrope of oxygen consisting of eight oxygen atoms.

As the pressure of oxygen at room temperature is increased through 10 GPa (1,450,377 psi), it undergoes a dramatic phase transition to a different allotrope. Its volume decreases significantly,[1] and it changes color from sky-blue to deep red.[2] This ε-phase was discovered in 1979, but the structure has been unclear. Based on its infrared absorption spectrum, researchers assumed in 1999 that this phase consists of O
4 molecules in a crystal lattice.[3] However, in 2006, it was shown by X-ray crystallography that this stable phase known as ε oxygen or red oxygen is in fact O
8.[4][5] No one predicted the structure theoretically:[6] a rhomboid O
8 cluster[7] consisting of four O
2 molecules.

Ball-and-stick model of O8
Part of the crystal structure of ε-oxygen

In this phase it exhibits a dark-red color, very strong infrared absorption, and a magnetic collapse.[8] It is also stable over a very large pressure domain[citation needed] and has been the subject of numerous X-ray diffraction, spectroscopic and theoretical studies. It has been shown to have a monoclinic C2/m symmetry and its infrared absorption behaviour was attributed to the association of oxygen molecules into larger units.

  1. ^ Akahama, Yuichi; Haruki Kawamura; Daniel Häusermann; Michael Hanfland; Osamu Shimomura (June 1995). "New High-Pressure Structural Transition of Oxygen at 96 GPa Associated with Metallization in a Molecular Solid". Physical Review Letters. 74 (23): 4690–4694. Bibcode:1995PhRvL..74.4690A. doi:10.1103/PhysRevLett.74.4690. PMID 10058574.
  2. ^ Nicol, Malcolm; K. R. Hirsch; Wilfried B. Holzapfel (December 1979). "Oxygen Phase Equilibria near 298 K". Chemical Physics Letters. 68 (1): 49–52. Bibcode:1979CPL....68...49N. doi:10.1016/0009-2614(79)80066-4.
  3. ^ Gorelli, Federico A.; Lorenzo Ulivi; Mario Santoro; Roberto Bini (November 1999). "The ε Phase of Solid Oxygen: Evidence of an O4 Molecule Lattice". Physical Review Letters. 83 (20): 4093–4096. Bibcode:1999PhRvL..83.4093G. doi:10.1103/PhysRevLett.83.4093.
  4. ^ Hiroshi Fujihisa; Yuichi Akahama; Haruki Kawamura; Yasuo Ohishi; Osamu Shimomura; Hiroshi Yamawaki; Mami Sakashita; Yoshito Gotoh; Satoshi Takeya & Kazumasa Honda (2006-08-26). "O8 Cluster Structure of the Epsilon Phase of Solid Oxygen". Physical Review Letters. 97 (8): 085503. Bibcode:2006PhRvL..97h5503F. doi:10.1103/PhysRevLett.97.085503. PMID 17026315.
  5. ^ Lars F. Lundegaard; Gunnar Weck; Malcolm I. McMahon; Serge Desgreniers; Paul Loubeyre (2006-09-14). "Observation of an O8 molecular lattice in the phase of solid oxygen". Nature. 443 (7108): 201–204. Bibcode:2006Natur.443..201L. doi:10.1038/nature05174. PMID 16971946. S2CID 4384225.
  6. ^ Cite error: The named reference epsilon was invoked but never defined (see the help page).
  7. ^ Steudel, Ralf; Wong, MW (2007). "Dark-Red O8 Molecules in Solid Oxygen: Rhomboid Clusters, Not S8-Like Rings". Angewandte Chemie International Edition. 46 (11). 2007-01-23: 1768–1771. doi:10.1002/anie.200604410. PMID 17450606.
  8. ^ Cite error: The named reference solid was invoked but never defined (see the help page).
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