DISCUSSION 107 



geometry and spatial distributioii ol the glyto^cn scattering. Now, as to 

 the question deahng with changes in quantmn yield with wavelength in the 

 case ol a pure substance, one never observes these changes. But in the case 

 of proteins in which there are complexities and wiiere there are various 

 kinds of residues al)sorbing you can have a change. 



Dr. Skligir: But this is not specifically the quantum yield of the particular 

 molecule that you are talking about. 



Dr. \Vebi:r: This is the quantum yield defined as the number of quanta 

 emitted di\ided by the number of quanta absorbed. I won't say anything 

 further. 



Dr. Rabinowitch: This may be an unfair question, but one to which Pro- 

 fessor Franck has referred at the beginning. What shall we think about the 

 alleged existence of low excited levels of protein— levels supposed to be 

 located only one electron volt above the ground state? 



Dr. Weber: I don't know whether any experiment which I have done on 

 fluorescence of proteins would be related to this question, to tell you the 

 truth. I prefer not to discuss it. 



Dr. Platt: I would like to comment on Dr. Rabinowitch's question. These 

 are awfully difficult experiments. There is no theoretical reason to expect 

 that there should be any electronic excitation levels in proteins lower than 

 tho.se that Dr. Weber has talked about. I think theorists would strongly 

 oppose the kind of results Healy has until they become confirmed by a 

 host of other laboratories with the best semi-conductor technique, oxygen- 

 free, free from false conductivity, from surface effects, etc. I don't believe 

 that one should believe in these low putative electronic states of proteins 

 yet. I think we would do better for a while to ignore them until there is 

 a lot better evidence. 



Dr. Rabinowitch: I am grateful for your permission to ignore them. 



Dr. Franck: Conclusions on the position of a conduction band and on 

 the quantum yield of photo-ionization are, according to newer studies, mostly 

 not reliable in so far as they refer to crystals or other ordered arrays of 

 organic molecules, and are based on the usual observations of photoconduc- 

 tivity. The greatest part of the observed conductivity, and often all of it, 

 is not caused by photo-ion i/ation of the molecules in the crystal, rather if; 

 is caused by electron donation of the cathode to the crystal, respectively 

 electron acception (i.e. hole production) at the anode. To avoid this effect, 

 it is in crystals of aromatic compounds not sufficient to shield the electrodes 

 against direct irradiation, if excitation movement can carry excitation energy 

 to the electrodes. 



Dr. Chance: Mr. Patrick Taylor reported at the Faraday Society results 

 on the possibility of conduction bands in cytochrome c and these results 

 make it even more unlikely that cytochrome c transfers electrons by means of 

 conductor bands. 



