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Singlet and triplet energy levels. When a singlet state nonradiatively passes to a triplet state, or conversely a triplet transitions to a singlet, that process is known as intersystem crossing. In essence, the spin of the excited electron is reversed.
A Jablonski diagram showing the excitation of molecule A to its singlet excited state (1 A*) followed by intersystem crossing to the triplet state (3 A) that relaxes to the ground state by phosphorescence. It was used to describe absorption and emission of light by fluorescents.
Most molecules encountered in daily life exist in a singlet state because all of their electrons are paired, but molecular oxygen is an exception. [1] At room temperature, O 2 exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive ...
Carbenes generally split into singlet carbenes and triplet carbenes, named for their spin multiplicities. Both have two non-bonding electrons; in singlet carbenes these exist as a lone pair and have opposite spins so that there is no net spin, while in triplet carbenes these electrons have parallel spins. [6]
O atoms have a triplet ground state. Methoxy cation has a triplet ground state. In a mass spectrometer, it dissociates into singlet products (formyl cation and H 2): CH 3 O + → H 2 + HCO + Numerous spin-forbidden reactions are encountered in transition metal chemistry since many metal ions can adopt multiple spin states.
The singlet-singlet transition between the two excited states is spin-allowed but parity-forbidden. The lower, O 2 (1 Δ g) state is commonly referred to as singlet oxygen. The energy difference of 94.3 kJ/mol between ground state and singlet oxygen corresponds to a forbidden singlet-triplet transition in the near-infrared at ~1270 nm. [12]
The ability of positronium to form both singlet and triplet states is described mathematically by saying that the product of two doublet representations (meaning the electron and positron, which are both spin-1/2 doublets) can be decomposed into the sum of an adjoint representation (the triplet or spin 1 state) and a trivial representation (the ...
2 molecule, the spins of the two hydrogen nuclei (protons) couple to form a triplet state known as orthohydrogen, and a singlet state known as parahydrogen. The triplet orthohydrogen state has total nuclear spin I = 1 so that the component along a defined axis can have the three values M I = 1, 0, or −1.