Triplet oxygen, systematically but less commonly,
1,2-dioxidanediyl, is a term that refers to normal, gaseous oxygen (O
2, dioxygen) in its
ground state. It is therefore classified as an
inorganic chemical, and more specifically as a particular
electronic state of one
allotrope of the inorganic chemical
element, oxygen. In this particular state, according to one type of modern
bonding theory, the
electron configuration of the oxygen
molecule has two electrons occupying two
molecular orbitals (MOs) of equal energy (that is,
degenerate MOs), therefore remaining
unpaired. These orbitals are classified as
antibonding and are of higher energy, so the resulting
bonding structure between the oxygen atoms is weakened (i.e., is higher in energy)—for instance, it is higher in energy than the bonding in di
nitrogen, where bonding MOs are filled instead. The spectroscopic molecular
term symbol for triplet (ground state) oxygen is
3S
g-.