Triplet oxygen

Triplet oxygen is molecular oxygen in its electronic ground state, with two unpaired electrons whose parallel spins give the molecule total spin one.

Molecular orbital theory: A model of molecules that describes electrons as occupying orbitals spread across multiple atoms. Its orbital filling predicts oxygen’s two unpaired electrons.
Combustion: A rapid exothermic reaction, usually between a fuel and an oxidizer, that releases heat and often light. Triplet oxygen is the oxidizer in ordinary flames, though ignition barriers govern its reactions.
Pauli exclusion principle: The quantum rule that identical fermions cannot occupy the same complete set of quantum states. It constrains how oxygen’s electrons fill molecular orbitals and pair their spins.
William Bragg: A British physicist who studied crystal structures and the magnetic properties of matter. His early magnetic measurements helped establish that oxygen molecules are paramagnetic.
Diatomic oxygen: The molecule O₂, composed of two oxygen atoms bonded together. Triplet oxygen is the ground electronic state of this molecule.
Autoxidation: A chain reaction in which a substance reacts with molecular oxygen without direct enzymatic control. Triplet oxygen initiates and propagates oxidation chains in materials such as oils.
Hund's rule: The rule that electrons occupy degenerate orbitals singly with parallel spins before pairing. It accounts for the parallel spins in oxygen’s partially filled antibonding orbitals.
James Franck: A German physicist whose work on electron-impact excitation helped establish quantum descriptions of atomic and molecular states. Franck and collaborators investigated oxygen’s electronic states through spectroscopy.
Spin quantum number: A quantum number that specifies the total intrinsic angular momentum of a particle or system. The two unpaired electron spins combine to give oxygen total spin one.
Lipid peroxidation: The oxidative chain reaction that damages lipids, especially polyunsaturated fatty acids in membranes. Oxygen-derived radicals carry out this chain reaction in biological membranes.

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