QUANTUM YIELD 



1945 



The dependence of quantum yield on [CO2] was found not only in acid 

 phosphate media, but also in alkaline carbonate buffers. In fig. 37D.27 

 the crosses correspond to two-vessel measurements in acid media of varying 

 carbon dioxide content, while circles are quantum yields derived from one- 

 vessel measurements in carbonate buffer, with [CO2] varied by changing 

 the total concentration and the bicarbonate-carbonate ratio. The highest 



0.36 



0.33 

 0.30 



an 



0.2^ 



w 



0.18 



0.15 

 0,12 

 0.09 

 0.06 

 0.03 



, y. 



W 



VJ 5.0 



0.5 W 1J5 2.0 2.5 3.0 3.5 



Fig. 37D.27. Quantum yield I/7 = ^.Ot/hv, as function of carbon dioxide con- 

 centration (in vol. %) at 20° C. (after Warburg, Geleick and Briese 1951). 

 Crosses, two-vessel measurements in acid medium; circles, one-vessel measure- 

 ments in carbonate-bicarbonate buffers. Abscissa, % CO2. Ordinate, y. 



conveniently accessible [CO2] value in carbonates corresponds to 2% CO2 

 in the atmosphere, and is reached in 0.2 M mixture of 95 parts bicarbonate 

 and 5 parts carbonate. (The buffering capacity of this mixture is rather lim- 

 ited but sufficient for an experiment of several hours duration.) In this 

 buffer, a quantum requirement of about 3.3 was observed, as compared to 

 9-10 in buffer No. 9 (0.1 71/, 85 parts bicarbonate -f- 15 parts carbonate buf- 

 fer, 0.2% CO2). Warburg suggested that this explains why Emerson (and 

 others) have never found minimum quantum requirements lower than 



