MULTISTAGE DEACTIVATION IN THE PHOTOLYSIS OF HEXAFLUOROACETONE

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Abstract
In principle the vibrationally excited molecule in an upper electronic state, formed by absorption in the ultraviolet region of the spectrum, can attain vibrational equilibrium by two mechanisms. In most discussions of this degradation of vibrational energy it has been considered that the data are represented adequately by a single-step deactivation from high to low vibrational levels rather than by a multistep cascade from one group of vibrational levels to the next lower group. The present work suggests new treatments of the experimental data by which it is possible to distinguish between the single- and the multi-step deactivation processes. It is demonstrated that the literature data on the quantum yield for the decomposition of hexafluoroacetone is better interpreted in terms of a multistep deactivation. Some new data are presented which support this conclusion.Methods to evaluate the efficiencies as deactivating agents of added inert gases are discussed. It is suggested that the deactivation of excited hexafluoroacetone by hydrocarbons might involve chemical rather than, or in addition to, purely physical quenching.

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