THEORETICAL AND ACTUAL MAXIMUM QUANTUM YIELD 1139 



(29.11) 70 = dP/d(k*Ch]oI) = keEln/ik' + A;.E°) 



In (29.9), the "forward" reaction of HX-Chl-Z with ACO2 competes 

 with the primary back reaction (conversion to X- Chi -HZ); in (29.11) 

 the stabiUzing "forward" reaction of AHC02-Chl- A'HO with the catalyst 

 Eb competes with the back reaction (conversion to AC02-Chl-A'H20). 

 In either case, the "theoretical" quantum yield, n, can be closel}^ ap- 

 proached only if the ratio A-'/AvA) (or k'/keE^a) is much smaller than 1. 



Recognition that the maximum observable quantimi yield may be smaller 

 than the theoretical quantum yield, n, was first reached in the derivations 

 of Franck and Herzfeld (1941) (c/. their Table 1). The reaction mecha- 

 nism used by them, although more complicated than the ones considered 

 here, also was based on competition between stabilizing forward reaction 

 and back reactions of the immediate reduction products. 



The analytical expressions may be more complicated, but the essential 

 result also remains the same if the effective back reaction is a secondary 

 one, such as (28.21d). If this reaction competes with the forward trans- 

 formation of the intermediate reduction product AHCO3 by the catalyst 

 Eb (or of the intermediate oxidation product A'HO by the catalyst Ec), 

 the fraction of the products that undergoes back reaction will remain finite 

 even when the forward reactions have the maximum possible rate con- 

 stants, i. e., when the full available amounts of the relevant catalysts are 

 free and can be utilized for transformation (as is the case in weak light). 



Bibliography to Chapter 29 

 The Light Factor. II. Maximum Quantum Yield of Photosynthesis 



1918 Willstatter, R., and Stoll, A., Untersuchungen iiber die Assimilation der 

 Kohlensdure. Springer, Berlin, 1918. 



1922 Warburg, 0., and Negelein, E., Z. phijsik. Chem., 102, 235. 



1923 Warburg, 0., and Negelein, E., ibid., 106, 191. 

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1925 Wurmser, R., AnJi. physiol. physicochimie bioL, 1, 47. 



1926 Wurmser, R., /. phys. radium, [II] 7, 33. 

 1929 Briggs, G. E., Proc. Roy. Soc. London, BIOS, 1. 

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