Effect of Added Quenchers in Organic Scintillator Solutions: Aromatic Halides

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Abstract
Luminescence‐intensity measurements, as affected by quencher concentration, solvent and scintillator, yield information on quenching constants, on specific rates of quenching, on mechanism of quenching, on contrast between quenching of solvent and quenching of scintillator, and on contrast between quenching in benzene as solvent and quenching in cyclohexane as solvent. For a number of aromatic bromides (and for iodobenzene), excitation transfer appears to be involved in the quenching process; in those cases the specific rates are higher than may be expected for simple diffusion‐controlled reactions. Typical specific rates (kq) are ≃ or >2.5×1010 M—1 sec—1 in benzene. The donor states from which excitation is transferred are not identified. In cyclohexane, calculated kq values are very much higher with an implication that the mechanism of the quenching process is quite different in such cases. Some of the results can be explained in terms of the theory of solvent domains; the data for cyclohexane suggest that the mechanism of deposition and localization of energy must also be carefully considered.