108 SPECTROSCOPIC INVESTIGATIONS 



yield under the conditions of the reaction is practically nil. Notwith- 

 standing the similarity, the chemiluminescence emission spectra are 

 generally broadened with respect to the fluorescence spectra, just as 

 in the case of the high-temperature spectrum of dimethylbisacridinium 

 nitrate. If this broadening of chemiluminescence spectra relative to 

 fluorescence spectra proves to be a general feature, it may be of con- 

 siderable theoretical interest. 



Our only conclusion from the results discussed above is that the 

 chemical structure of the emitting molecule is similar to that of the 

 acid, diketo form of the derivatives of DPD. As the absorption spectra 

 of these compounds are not very characteristic, a further identification 

 is impossible, and in particular it is not possible to decide whether or 

 not the heterocyclic ring is still intact in the emitting molecule. Its 

 structure may be represented therefore by a general formula of the 

 type 



O 



/C— R 



C— R' 



O 



The interpretation of chemiluminescence spectra touches upon the 

 question of the reaction mechanisms and the occurrence of interme- 

 diate products. Attractive as this aspect may be, it is surprising that 

 so little is known about it with certainty. 



We will now turn to the examination of the emission spectra of 

 luminous organisms. From the foregoing we may expect them to be 

 related to fluorescence spectra of reaction products of the molecules 

 entering into the luminescent reaction. Hence they should show 

 vibrational structure only in so far as the fluorescence spectra and in 

 particular also the longest-wavelength bands in the absorption spectra 

 of the compounds involved show such vibrational structure. The 

 occurrence of secondary maxima, such as those found by Eymers and 

 van Schouwenburg (1937), in emission spectra of various types 

 should be of special interest. We regret to say that more careful 

 measurements have failed to confirm the claims of these authors. 



