MELVIN CALVIN 353 



phyll (and chlorophyll model substances) , namely, the transfer of 

 an electron, or hydrogen atom, from the excited porphyrin to an 

 electron acceptor at a liigli reduction level which can be used to re- 

 duce the ultimate carbon dioxide reducers, followed by the donation 

 of an electron, ultimately from water, to the remaining radical ion, 

 or lattice, which produces the net result of the transfer of hydrogen 

 from water to carbon dioxide. 



How much of the solid state picture will be required to fully 

 imderstand this separation of oxidant and reductant I think is yet 

 to be determined. However, I believe it is quite clear that we are 

 coming to the same kind of conclusion from both ends, that is, from 

 both the pure solution chemistry which involves electron transfer 

 from donor to acceptor, and from the solid state experiments which 

 involve the same kind of electron transfer from donors to acceptors. 

 The difference lies in the types of lattices involved. The back-reaction 

 in the solid state experiments is demonstrably slower than one can 

 visualize for the solution electron transfer reaction in which no 

 provision is made for the rapid, relatively temperature-independent 

 separation of the products, electron (reducing agent) and hole (oxi- 

 dizing agent) . 



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