107 



James Franck and J. L. Rosenberg 



700 



ove length in m>j 



Fig. 1. Absorption spectriom of chlorophyll a in 

 ether 10-5 M^ cijrve 2; of colloidal chlorophyll 

 siispension in JOfo aqueous methanol, crosses of 

 curve 1. Curves from reference (l5)- 



of the long wave-length peak in their "colloidal" samples in 

 comparison with monomeric material. Of the three chlorophyll a 

 components fo\and by French and Brown(l6)^ ve ascribe the main 

 peak at about 67O to the amorphous chlorophyll, and the two 

 minor peaks at about 68O and 7OO m\x to the two differently polar- 

 ized Davydov components of the crystalline chlorophyll. We note 

 that the relative proportions of crystalline to non- crystalline 

 chlorophyll may vary with ciiltixring conditions and need have no 

 particular stoichiometric value. Also, the extent of the absorp- 

 tion shift depends on the size of the microcrystallites'lT j and 

 a distribution of crystal size woiiLd be expected to cause broad- 

 ening of the bands. 



If OTor scheme makes possible a self-consistent explanation of 

 the Emerson effect, it must provide the answer to five questions. 



a) Why does the photosynthetic quantum yield fall in the far- 

 red with increasing wave-length of absorption in the crystalline 

 regions? 



