Wigners spin conservation rule

This is an example of the Wigner spin conservation rule (p. 316). Note that spin conservation is something entirely different from symmetry conservation. 

Table 6.1 Some energy-transfer processes by the electron-exchange mechanism allowed according to the Wigner spin conservation rule...

Energy transfer by the exchange mechanism will occur provided the spin states before and after overlap obey the Wigner spin conservation rule that is, provided the overall spin states before and after overlap have common components (Table 6.1). 

A reaction between two species (Le., atoms or molecular entities), both of which are in triplet electronic states, resulting in at least two products, one of which is in its ground singlet state and the other in an excited singlet state. Delayed fluorescence often accompanies such processes. See also Annihilation Wigner Spin Conservation Rule Delayed Luminescence... 

WIGNER SPIN CONSERVATION RULE DELAYED LUMINESCENCE TRIPLET-TRIPLET ENERGY TRANSFER TRIPLET-TRIPLET TRANSITIONS TRITIUM TRITON TRITIUM... 

PROTEIN TURNOVER KINETICS WIGNER SPIN-CONSERVATION RULE WOMACK-COLOWICK DIALYSIS METHOD WORK... 

Equations (5-6) and (5-7) are the spin-free analog of the Wigner spin-conservation rule. The only total permutational symmetries [A] which may arise from molecules with permutational symmetries [Aa] and [AB] are given in the sum of eq. (5-6). Examples for certain cases of [Aa] and [Ab] are given in Table III. Using the correspondence eq. (2-14) between... 

Spin-Free Wigner Spin Conservation Rules ... 

Two additional complications may be present in photochemical reactions, the presence of hot molecules and hot radicals referred to earlier in thermal systems, and the possible physical and chemical primary processes that may occur. Compounds such as biacetyl, O2, NO and olefins are particularly efficient quenchers of electronically excited species. In accordance with the Wigner spin conservation rule that the total spin in a quenching process is conserved, triplet state acetone ( A) is quenched very efficiently to the ground state ( A) by olefins (O) . 

In any transfer of electronic energy between an excited species and a ground state species, the overall spin angular momentum does not change. Thus, energy transfer is subjected to the Wigner spin conservation rule. In photosensitisation, there are following allowed spin possibilities. 

Fig. 8.11 Wigner spin conservation rules used to calculate the probability of aU contact interactions...

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