Diagram of a molecule of this compound (top)
Ultritium 283 is a form of ultritium, one of many explosive materials available to the crew of the USS Enterprise-D in 2367 when they were trapped in a Tyken's Rift.
According to the database, this material is an "industrial chemical explosive used in mining applications intended for precision-charge patterns using standard microwave pulse ignition devices." (TNG: "Night Terrors")
Atoms of this material appeared in an okudagram display of explosives listed in the Enterprise-D library computer.