108 RADIATION BIOLOGY 



Table 2-3. Adopted Spectroscopic Moments for Porphin Substituents 



Isocyclic rings connecting 7-6 positions 



-CH2— CO— 

 -CH(C00CH3)— co- 



Like 7— CH3 plus 6— COOH 

 Like 7— CH3 plus 6— COOH 





" Used in summarizing the structure of the compounds in Fig. 2-23. 



which can be obtained from the area under the absorption curve for the 

 whole electronic transition. Estimates of this area in a few cases indi- 

 cate that Q is about 30 per cent larger in the porphins than in the ben- 

 zenes. The difference may indicate a greater polarizability of the porphin 

 ring system. 



Figure 2-21 shows how the vector moments are added to give the 

 resultant moment for a few compounds. The direction of the resultant 

 is shown with respect to the H-H axis. This should be the direction of 

 polarization of the absorption or emission and may be experimentally 

 tested if oriented crystals of the compounds are available. The direc- 

 tions of polarization of the two electronic components are no longer neces- 

 sarily perpendicular after substitution has destroyed the symmetry. 



Intensity Formulas. The fact that the individual moment vectors are 

 at right angles enables us to write simple formulas for the total change of 

 intensity of band I or l)and TIT. T^et 



m\ + m-„ = M i\ in-i + m^, = M2', 

 m?, + ni-i = ilfs; W4 + mg = M a] 

 ma + m^ -\- niy -\- nn = Ma\ mN, + rriN, = rriN, + m.v, = Mn. 



