An apparatus has been designed and built for the study of low fluorescence intensities. The ``blue'' fluorescence of acetone vapor has been investigated from pressures of about 1 mm to pressures of about 200 mm, at temperatures from 25°C to 300°C both with and without the addition of foreign gases, such as O2, NO, N2, and (CH3CO)2.It is found at temperatures over about 100°C, and in the presence of O2and NO, that there is no structure in the fluorescence of acetone which can be detected, and the wavelength of the intensity maximum is different from that found at 25°C. The shapes of the quenching curves are such as to demand at least two upper electronic states which participate directly or indirectly in the fluorescence phenomenon. This is in agreement with previous work. The photo‐chemical data necessitate a high probability of predissociation of the initially formed state together with a small lifetime probably determined by the rate of predissociation. At least one other upper state, formed from the first through collisions, must be relatively insensitive to collisional deactivation. A complete theory cannot be given, but some important aspects are clear.
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