460 Discussion 



vibrational structure. Moffitt (/. chem. Phys. 22, 320, 1954) has shown how the differ- 

 ence in coupling between two electronic states and the vibrational states can arise 

 through the change in symmetry property of the ground as compared with the two 

 excited states. Until it is known that symmetrical porphyrins do not show vibrational 

 structure of the a- and /?-bands it will not be safe to look for explanations in terms of 

 the ground state symmetry of the ring. 



