The Mechanism of Processes Initiated by Excited Atoms II. Photosensitization by Excited Mercury and Cadmium

Abstract

The treatment of the preceding paper is extended to the reactions of excited mercury and cadmium in their triplet and singlet states. It is shown that with the hydrogen molecule quenching of a physical nature is prohibited for the triplet atoms by the necessity for conservation of spin angular momentum, and that dissociation must take place with the initial formation of the metal hydrides. In the reactions of Hg ³P₀, Cd ³P₁, and Cd ³P₀ these are also final products, but with Hg ³P₁ and the singlet excited atoms, dissociation of the hydride into the metal and a hydrogen atom takes place at once. Quenching to the metastable state is found to be usually inefficient. The atoms react with saturated hydrocarbons by splitting off a hydrogen atom, but the unsaturated ones usually interact with the initial formation of an excited molecule which when activated by singlet atoms have vibrational energy only, but which with triplet atoms are excited to triplet electronic states. The subsequent reactions of the excited olefines are discussed with reference to the experimental material.