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Measurements are described of the Stern-Volmer quenching constants for oxygenand self-quenching of the fluorescence of certain aromatic hydrocarbons and derivatives, in the vapour state and in benzene, chloroform, and kerosene solutions. Quantum yields of fluorescence and estimates of mean lives of the excited molecules are also presented and from them absolute rates of quenching are derived. The vapour state results show that quenching occurs in a high proportion of molecular collisions. For the solutions the absolute quenching rates are compared with calculations of encounter rate, and the value of the results in understanding collision processes in liquids is discussed.

Measurements are given of quantum efficiencies of dimerization of anthracene, and of photo-oxidation of anthracene and diphenylanthracene, in solution in various solvents at different oxygen concentrations. A kinetic scheme capable of accounting for the results is presented.Anthracenes show three types of photo-reaction in solution, dimerization (of some anthracenes), photo-oxidation to peroxides, and reactions with the solvent.

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