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Examples of atoms in singlet, doublet, and triplet states. In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin S = 1. It has three allowed values of the spin's projection along a given axis m S = −1, 0, or +1, giving the name "triplet".
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 ...
The radiative decay from an excited triplet state back to a singlet state is known as phosphorescence. Since a transition in spin multiplicity occurs, phosphorescence is a manifestation of intersystem crossing. The time scale of intersystem crossing is on the order of 10 −8 to 10 −3 s, one of the slowest forms of relaxation. [3]
Singlet oxygen refers to one of two singlet electronic excited states. The two singlet states are denoted 1 Σ + g and 1 Δ g (the preceding superscript "1" indicates a singlet state). The singlet states of oxygen are 158 and 95 kilojoules per mole higher in energy than the triplet ground state of
In the ground state of dioxygen, this energy level is occupied by two electrons of the same spin, as shown in the molecular orbital diagram. The molecule, therefore, has two unpaired electrons and is in a triplet state. In contrast, the first and second excited states of dioxygen are both states of singlet oxygen. Each has two electrons of ...
The triplet state has total spin quantum number S=1 and is paramagnetic. [5] Therefore, diradical species display a triplet state when the two electrons are unpaired and display the same spin. When the unpaired electrons with opposite spin are antiferromagnetically coupled, diradical species can display a singlet state (S=0) and be diamagnetic. [6]
The spin relationship is such that the two unpaired electrons, one in each radical molecule, may have opposite spin (singlet; anticorrelated), or the same spin (triplet; correlated). The singlet state is called such because there is only one way for the electrons’ spins to anticorrelate (S), whereas the triplet state is called such because ...
Cyclobutane-1,3-diyl is the planar four-membered carbon ring species with radical character localized at the 1 and 3 positions. The singlet cyclobutane-1,3-diyl is predicted to be the transition state for the ring inversion of bicyclobutane, proceeding via homolytic cleavage of the transannular carbon-carbon bond (Figure 3).