100 



SPECTROSCOPIC INVESTIGATIONS 



nature, consisting of broad bands in which vibrational and rotational 

 fine structure is almost always lacking. Moreover, in the case of 

 emission spectra such as fluorescence spectra, the observed emission 

 band corresponds to only one electronic transition in the molecule so 

 that such spectra are even less detailed than the absorption spectra. 

 This does not take away the fact that in the study of bioluminescence, 

 the emission spectra are the only data obtainable that are immediately 

 and uniquely connected with the bioluminescent compounds. In this 

 connection, an accurate knowledge of spectra should be highly 

 desirable. 



Li 

 0) 



::=;: 



Abs 



riuor 



A 



/(i\ n\ 



'Xrt 



\ 



Fluor. 'i Abs. 



Distemce 



Fig. 1. a and b. Energ>' states for a two-atom molecule with transitions in ab- 

 sorption and fluorescence, c. The occurrence of mirror symmetry between 

 absorption and fluorescence spectrum. 



It needs no emphasis that bioluminescence is a form of chemilu- 

 minescence. The known chemiluminescent systems offer a means of 

 studying the relation between the chemiluminescence emission spec- 

 trum and other spectral properties of the compounds involved. During 

 the chemiluminescent reaction, molecules are transferred to an excited 

 state, and this is followed by the emission of light. Therefore, the 

 process of light emission during a chemiluminescent reaction is re- 

 lated to the light emission during fluorescence. It is therefore desirable 

 to say a few words at this point about the nature of fluorescence and 

 its relation to light absorption in organic molecules. We will consider 

 the case of a two-atom molecule. In Fig. la, two electronic energy 

 states of this molecule are given, together with some vibrational levels. 

 The arrows indicate a transition from the ground level to a higher 



