Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

Abstract

Studies have been made of the variation with ketone pressure of the quantum yield for the decomposition of hexafluoroacetone, excited by 3130 Å, at 25 and 78 °C, and of the relative yield of the total emission at several temperatures. These are described in considerable detail with a view to discerning possible sources of systematic error. No large systematic error could be identified except that of decreased yields caused by deactivation by mercury vapor. The decomposition data support the weak collision mechanism for vibrational relaxation in the excited singlet state unless an as yet unknown source of large systematic error can be identified.A description is offered of the path of the decomposition in terms of simplified diatomic representations of the nπ* singlet and triplet states and of a repulsive state arising from the radicals CF3 and CF3CO in their ground electronic states. On the basis of that description an activation energy ≥ 11 kcal mole−1, derived from the combined decomposition and emission data, is to be ascribed to the first-order decomposition of triplet state molecules in vibrational equilibrium with their surroundings.