102 



SPECTROSCOPIC INVESTIGATIONS 



countered that correspond to the long-wavelength absorption band in 

 the absorption spectrum. In Figs. 2 and 3, examples are given of this 

 mirror symmetry between absorption and fluorescence for some com- 

 pounds of interest in connection with the following discussion. For a 

 discussion of fluorescence of organic compounds the reader is referred 

 to Forster (1951). 



Returning to the chemiluminescence spectra, the question arises as 

 to the mechanism of excitation. We may visualize two possibilities: 



=EES::3 



330 



370 



410 



450 



490 



570 rryj 



Fig. 3. Mirror symmetry in the fluorescence and absorption spectra of methyl- 

 acridone. 



during the reaction, intermediates or end products are directly formed 

 in an excited state, or they may obtain their energy by transfer from 

 other reactants containing sufficient energy. It is not easy to distinguish 

 experimentally between these possibilities. 



Kautsky ( 1943 ) is believed to have shown that the emission spectra 

 of various chemiluminescent reactions were very similar to the fluores- 

 cence spectra of the parent compounds. This has led many investi- 

 gators to the assumption that during the chemiluminescent reaction, 

 the original molecules are regenerated, but in an electronically excited 



