PRIMARY PROCESSES IN ACETONE PHOTOCHEMICAL SYSTEM

A revised mechanism which quantitatively correlates the data for the principal emission (phosphorescence) and the dissociation primary processes in the acetone photochemical system is presented. Two decomposition processes are proposed, a spontaneous decomposition from upper vibrational levels of hot triplets formed isoergotically after light absorption, and a decomposition of thermalized triplets which is a unimolecular pressure-dependent process. Quite consistent high- and low-pressure Arrhenius parameters for the thermal decomposition are determined from several data sources and place the critical barrier to triplet decomposition at about Eo ≃ 10 ± 1 kcal/mol. When treated in accordance with the proposed mechanism, a quantitative correlation of the emission and the decomposition data in terms of their temperature, pressure, and wavelength dependencies is demonstrated. The zero-point level of the acetone triplet is placed at about 80 kcal/mol above the acetone ground state.