Quantum yield, definition with radicals

Some quantum yields of radical polymerization (< >p for definition see Eq. (2b)) with the model monomer MM A are presented in Table 5. It is obvious that a variety of parameters acts on this value. Mainly, the participation of initiator molecules and of primary radicals on chain termination are responsible for the differences in the < >p-values. 

The quantum yield 0 of a photophysical or photochemical event is a quantitative measure of the overall efficiency of this process (Braun et al., 1991). It is a unitless constant, which usually ranges from zero to one. However, some authors express 0 in units of mol einstein, which in fact is unit-less, because an einstein is defined as one mol of photons. Quantum yields greater than one indicate photo-induced chain reactions, which may involve radical species or photo-generated catalysis. Commonly used definitions of 0 are collected in Tab. 3-7. These definitions describe quantum yields of photophysical events and of photochemical reactions with regard to the reactant diminution or to the formation of the photoproduct Quantum yields may be dependent on the wavelength of the absorbed UV/VIS radiation, but many photochemical systems exist that have a constant quantum yield 0 over a defined wavelength range. Such chemical systems can be... 

Another feature of interest is related to the quantum yields of hydrogen peroxide and of ozone photochemistry as is outlined in Fig. 6-12. Theoretically, the photolysis of 1 mol of H2O2 should produce 2 mol of hydroxyl radicals with a calculated maximum quantum yield of two, according to the definition of presented in Tab. 3-7 = However, the experimental situation is much... 

With respect to our definition of photoassisted reactions also catalyzed photolyses are covered by this category. It was shown very recently [42] that the quantum yield of the well known photo decomposition of ferrioxalate is increased in the presence of copper(II) ions. Here, copper(II) in the ground state acts as a catalyst. Mechanistically, it is assumed that copper(II) accelerates the decomposition of the coordinated oxalate anion radical in the intermediate iron(II) complex. Copper(I) formed thereby is reoxidized in a thermal reaction by another ferrioxalate ion. In the absence of copper(II) the intramolecular back electron-transfer within the intermediate iron(II) complex is responsible for quantum yields lower than the theoretical limit. 

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