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plane of the paper and would extend only slightly above and below. 

 Because S state (that is, A = 0) implies spherical symmetry, this state 

 is ruled out. The next lowest possibility energywise is a II state. 

 Accordingly, the electrons not bound to a particular atom must be in n 

 states. These it electrons are believed to be responsible for the character- 

 istic spectra of most biologically interesting molecules. 



One approach to quantum mechanical models of more complex 

 molecules is the so-called " method of 'molecular orbitals." In this method, 

 one needs X-ray or other data describing where the atoms are located. 

 The "innermost" electrons (for example, the K shell of C and N) are 

 assumed to be undisturbed and are described by the same wave functions 

 and charge distributions as in the free atoms. Next, one forms linear 

 combinations of the wave functions representing the valence electrons 

 in the free atoms. The form of the new functions is restricted by 

 symmetry requirements and by other considerations. Finally, suitable 

 approximations can be made and constants can be adjusted until the 

 new computed orbitals predict the observed molecular properties. 

 Many chemists and physicists have felt that this method has revealed 

 important information about the molecule. Others feel the necessary 

 approximations and the adjustment of the constants limit the validity 

 of this method of molecular orbitals. In recent years, this method has 

 been used to produce wave functions (that is, molecular orbitals) which 

 correctly predict the spectra of tetrapyrrole ring structures and other 

 dyes. 



As far as basic information regarding the structure of molecules is 

 concerned, the infrared studies have yielded much more information 

 than those involving the absorption of light in the visible and ultra- 

 violet regions. However, as a physical tool for research and analysis, 

 the visible and ultraviolet spectra have been far more useful. These 

 spectra have been determined purely empirically. The maxima of the 

 characteristic absorption spectra are used for routine assays, kinetic 

 studies, and analysis of new compounds in all phases of biochemistry 

 and biophysics. By analogy, the use of the absorption peaks is similar to 

 distinguishing that one person is speaking German, another French, 

 and a third Chinese without understanding enough of their words to 

 comprehend what they are saying. Most of the information inherent 

 in the pattern of the absorption peaks is lost because no one can decode 

 it in terms of the electronic configurations of the molecule. 



REFERENCES 



1. This book is recommended especially for physics students interested in the 

 philosophical basis of quantum mechanics. 



