True differential quantum yield

1 True differential quantum yield The true differential quantum yield 

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First, we note that the number of photons absorbed rather than the number of incident photons has to be taken into account. Second, integrations over extended time periods most likely bear substantial errors because the intensity of the source may fluctuate or drift. As a consequence of this, the only exact measure for the efficiency of a photochemical reaction is the true differential quantum yield, which needs to be determined for each step of the reaction. Similar to thermal reactions, photochemical reactions may be complex. Accordingly, the only correct measure is the so-called partial (true differential photochemical) quantum yield, which is defined for each linearly independent step of the reaction. 

The true differential quantum yields can no longer be localised in the integrated equations of photokinetics. The different rate constants are distributed to different terms in the equation. On the other hand one can correlate quantum yields in the differential equations. If the quantum yield does not depend on the intensity of the irradiation source on finds according to eq. (3.35)... 

The true differential quantum yield has been symbolised as

quantum yields can be determined using eq. (5.20) ... 

One of the most important features of a photoreaction is the value of the quantum yield ( )i of compound i, which is the quantifying answer to the question How effective In principle, the quantum yield is the ratio of the number of reacting molecules to the number of quanta absorbed. In praxis there are several definitions of the quantum yield true (only light absorbed by the reactant is considered) and apparent (there are other absorbers present), differential (at the moment ) and integral (mean). In the previous rate equation, ( )e and (j) are the true differential yields. The monoexponential kinetics of Equation, 1.2 or 1.4 allow one to determine the yields in systems where the starting solution is already a mixture of E- and Z-forms (which can happen easily if the E-form is not prepared under strict exclusion of light). It turns out, however, that the yalues of the Z —> E quantum yield are especially sensitive to small errors in the E values. 

In the following the use of the term quantum yield implies that it is either a true differential or a partial one however, another special definition is given. Derivations are carried out for thermal reactions and dependencies demonstrated and explained. This is just a matter of simplicity, since in the application of the formalism the photochemical quantum yields in contrast to the rate constants contain potential dependencies on the mechanism. This is demonstrated in Chapter 3 for complex reactions. 

Section 2.1.2 demonstrated that the quantum yields depend on the concentration of the reactants in a characteristic way (in general the true differential and the partial quantum yields respectively). Iliis correlation can be used for kinetic analysis. 

Where the Schrodinger or Dirac equations apply, quantization will appear from sundry mathematical conditions on the existence of physically meaningful solutions to these differential equations. However, in nonrela-tivistic terms, spin does not come from a differential equation It comes from the assumptions of spin matrices, or from "necessity" (the Dirac equation does yield spin = 1/2 solutions, but not for higher spin). So we must posit quantum numbers (see Section 2.12) even when there are no differential equations in the back to "comfort us." This is especially true for the weak and strong forces, where no distance-dependent potential energy functions have been developed. 

The Schrodinger equation for even a single /V-electron atom is a partial differential equation with 3N variables, and to make matters worse, the interelectron interaction causes the solutions to be true 3/V-dimensional functions that cannot simply be broken down into smaller constituent parts. Nevertheless, despite the staggering complexity of even small-sized systems, quantum theory has yielded great success in calculating useful properties of complex systems and in producing... 

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