for his help in obtaining and interpreting the n.m.r. spectra. We also extend thanks to Mr. J. W. Coryell, who aided us in the cryoscopic and surface tension measurements.

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The fluorescence spectra of europium and terbium /3-diketone chelates are modified significantly on changing substituents in the organic ligand. The relative intensity, spectral distribution, shifting, and splitting of the fluorescence lines are discussed in relation to the nature of substituents, their position, molecular configuration, and the over-all intramolecular energy transfer.

l-(Phenylhydroxymethylene)-4-(dimethylhydroxymethyl)-2,5-cyclohexadiene is proposed to be the stable intermediate (In) in the photoreduction of benzophenone in pure isopropyl alcohol. The phosphorescence and phosphorescence excitation spectra of In were obtained by matrix isolation in frozen isopropyl alcohol at 77°K.The absorption spectrum of in determined by the use of actinometry and verified by the excitation spectrum was used to follow the kinetics of the dark reaction following irradiation. The proposed mechanism is consistent with all observed data and explains the erratic quantum yield results reported previously. dal, Charles Hurt, and George Mushrush for their assistance in the experimental work and the National Aeronautics and Space Administration for partial support under Grant NsG-603.

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