What is "triplet oxygen"

n. (context physics chemistry English) the normal state of molecular oxygen

Triplet oxygen, systematically but less commonly, 1,2-dioxidanediyl, is normal, gaseous oxygen (O, 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 the corresponding antibonding orbitals are empty. The spectroscopic molecular term symbol for triplet (ground state) oxygen is Σ.