SPECIFICITY OF LONDON-EISENSCHITZ-WANG FORCE 59 



provided their polarizabilities are strong enough according to the criteria laid 

 down in the paper. Let me come back to your question in a few moments. 



Professor Pitzer: But surely we know the visible and most of the other 

 important regions of the spectrum for these substances, so this is essentially 

 an answerable question, is it not? 



Professor Kirkwood (Yale University): I was just going to ask the same 

 question as Professor Pitzer. You are definitely excluding structural vibra- 

 tions; you admit that the magnitudes of the effects are too small in those in- 

 stances. 



Professor Jehle: As concerns the usual structural vibrations effects, their 

 polarizabilities are very small indeed, so we can ignore them. There are, how- 

 ever, some very strong absorption bands in the 3 ju region in liquid H2O (Earl 

 K. Plyler and N. Acquista, J. Opt. Soc. Am. 1954. 44: 505-506) and correspond- 

 ingly proteins and nucleic acids in their natural aqueous surrounding are ex- 

 pected to have some interesting absorption in that region. Before the intensity 

 of this band is actually established and before the cause for the unexpected 

 strength of this band is understood, I hesitate to state that its significance for 

 London interactions is negligible, even though on a first inspection this band 

 makes but a small contribution. As concerns the charge fluctuations which 

 Kirkwood and Shumaker have investigated, they contribute very strongly to 

 our Wo terms, if one uses the magnitudes of the terms proposed by these 

 authors, so that even if their estimated values would have to be reduced, there 

 still would be a most significant contribution to our Wq values. Anisotropy 

 will lend itself to providing for several Wo components. 



Professor Kirkwood: In regard to the second remark of Professor Pitzer, 

 there is some argument about the positions of the electronic states in macro- 

 molecules such as protein which is connected with proposals, which I do not 

 think are accepted, that one may have, due to conjugation or hyperconjugation 

 of some sort, a band structure analogous to that in metals. If one has that, 

 then your considerations might apply. However, it is probably true that the 

 ground electronic state of macromolecules, such as proteins and probably nu- 

 cleic acids, are nondegenerate and that the first energy of excitation is too high 

 to be excited under ordinary conditions of experimentation and ordinary tem- 

 peratures. 



There is another point I want to bring up. It is also true that in the case of 

 macromolecules (and this was pointed out by London and elaborated upon by 

 Overbeek), quite apart from the Casimir corrections, it is not a very good ap- 

 proximation to expand the interaction into multipole terms when the separation 

 between the centers is comparable with the dimensions of the molecules. Lon- 

 don, himself, pointed out something which has not been exploited to any great 

 extent. That is, probably it is only important in conjugated systems where one 

 does have resonance extending over a fairly large distance that one can get 



