Exotic atoms

neutral composite particle with some components not found in normal atoms

alt=Simplified drawing of the muonium atom|thumb|300x300px|A muonium atom

Di-positronium, or dipositronium, is an exotic molecule consisting of two atoms of positronium. It was predicted to exist in 1946 by John Archibald Wheeler, and subsequently studied theoretically, but was not observed until 2007 in an experiment performed by David Cassidy and Allen Mills at the University of California, Riverside. The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silicon dioxide. Upon slowing down in the silica, the positrons captured ordinary electrons to form positronium atoms. Within the silica, these were long l

chemical compound

exotic atom consisting of a negatively charged kaon orbiting a proton

exotic matter with an antiproton in place of an electron