Editing Positronium (section)

== Exotic compounds ==

Molecular bonding was predicted for positronium.<ref>
{{cite journal
 |title=Signature of the existence of the positronium molecule
 |arxiv=physics/9804023
 |last1=Usukura | first1=J.
 |last2=Varga | first2=K.
 |last3=Suzuki | first3=Y.
 |date=1998
 | doi=10.1103/PhysRevA.58.1918
 | volume=58
 | issue=3
 | journal=Physical Review A
 | pages=1918–1931
 |bibcode=1998PhRvA..58.1918U|s2cid=11941483
 }}</ref>  Molecules of [[positronium hydride]] (PsH) can be made.<ref>{{cite web|url=http://www.sc.doe.gov/bes/accomplishments/files/BES_Accomp_FY1992.pdf|page=9|title="Out of This World" Chemical Compound Observed|url-status=dead|archive-url=https://web.archive.org/web/20091012090920/http://www.sc.doe.gov/bes/accomplishments/files/BES_Accomp_FY1992.pdf|archive-date=2009-10-12}}</ref>  Positronium can also form a cyanide and can form bonds with halogens or lithium.<ref name="Saito">{{cite journal|last=Saito|first=Shiro L.|date=2000|title=Is Positronium Hydride Atom or Molecule?|journal=Nuclear Instruments and Methods in Physics Research B|volume=171|pages=60–66|doi=10.1016/s0168-583x(00)00005-7|bibcode = 2000NIMPB.171...60S|issue=1–2}}</ref>

The first observation of [[di-positronium]] ({{chem2|Ps2}}) [[molecule]]s—molecules consisting of two positronium atoms—was reported on 12 September 2007 by David Cassidy and Allen Mills from [[University of California, Riverside]].<ref>
{{cite journal
 |last1=Cassidy |first1=D.B. |last2=Mills |first2=A.P. (Jr.)
 |date=2007
 |title=The production of molecular positronium
 |journal=[[Nature (journal)|Nature]]
 |volume=449 |pages=195–197
 |doi=10.1038/nature06094
 |pmid=17851519
 |issue=7159
 |bibcode = 2007Natur.449..195C |s2cid=11269624 }}</ref><ref>
{{cite journal
 |author=Surko, C.
 |date=2007
 |title=A whiff of antimatter soup
 |journal=Nature
 |volume=449
 |issue=7159
 |pages=153–155
 |doi=10.1038/449153a|pmid=17851505
 |s2cid=8153916 
|doi-access=free
 }}</ref><ref>
{{cite web
 |url=http://www.physorg.com/news108822085.html
 |publisher=[[Physorg.com]]
 |title=Molecules of positronium observed in the lab for the first time
 |access-date=2007-09-07
}}</ref>

Unlike [[muonium]], positronium does not have a nucleus analogue, because the electron and the positron have equal masses.<ref name=barnabas/> Consequently, while muonium tends to behave like a light isotope of hydrogen,<ref>{{cite journal |last1=Rhodes |first1=Christopher J. |date=2012 |title=Muonium–the second radioisotope of hydrogen: a remarkable and unique radiotracer in the chemical, materials, biological and environmental sciences |journal=Science Progress |volume=95 |issue=2 |pages=101–174 |doi=10.3184/003685012X13336424471773 |pmid=22893978 |pmc=10365539 }}</ref> positronium shows large differences in size, polarisability, and binding energy from hydrogen.<ref name=barnabas>{{cite journal |last1=Barnabas |first1=Mary V. |last2=Venkateswaran |first2=Krishnan |last3=Walker |first3=David C. |date=January 1989 |title=Comparison of muonium and positronium with hydrogen atoms in their reactions towards solutes containing amide and peptide linkages in water and micelle solutions |journal=Canadian Journal of Chemistry |volume=67 |issue=1 |pages=120–126 |doi=10.1139/v89-020 |doi-access=free |bibcode=1989CaJCh..67..120B }}</ref>