Fluorescence, phosphorescence and decomposition

Oxygen decreases the efficiency of the emission at high oxygen concentrations a limiting yield is attained which is dependent on the acetone pressure but independent of the temperature. Oxygen, like the increase in temperature, eliminates the structure of the spectrum and shifts the intensity maximum towards shorter wavelengths . Nitric oxide exerts a similar influence to Oj. 

At least two upper electronic states have to be assumed when interpreting the luminescence results. Evidently, the electronic state eliminated by the temperature increase is the same as that quenched by oxygen or nitric oxide. 

Finally, it should be mentioned that acetone itself quenches both its excited singlet and triplet states. A Stern-Volmer relation is obeyed by the self-quenching of phosphorence and probably of fluorescence as well .  

We discuss now, in brief, the photophysical processes occurring as a result of irradiation. (The system of notation used has previously been described, p. 284.) 

As a consequence of light absorption, excitation to the vibrationally excited upper singlet state occurs, viz. 

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