S/DXEY I'. VELICK 



HI 



describe the excitation spectrum for the lliiorescence. A curve ot tliis 

 type was first obtained by Weber ('^D) . The strong excitation band 

 at 2()() ni/x, where more than 90 per cent ot the light is absorl^ed 

 by adenine, could only arise by the transfer of excitation energy from 

 adenine to pyridine. The lifetime of the adenine excited state, a 

 singlet state, is very short, since adenine fluorescence is not observed 

 in neutral aqueous solutions at room temperature. Therefore, for 



300 340 380 

 Excitation, mu 



Fig. 3. 1 he fluorescence excitation specirimi of DPNH in water as a function 

 of temperature. .\s in Fig. 2, the spectra are corrected to correspond to an ex- 

 citation beam of constant intensity as a function of wavelength. The tempera- 

 ture effects are completely reversible. 



