Cadmium-Photosensitized Interconversion of cis-, trans-, and geminal-Ethylene-d2

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Abstract
Quantum yields of the reactions following quenching of Cd (5 3 P 1 ) atoms by cis‐, trans‐, and geminal‐ethylene‐d 2 have been determined at 325°C and ethylene pressures of 3 and 13.5 torr. Cis–transisomerization and intramolecular hydrogen scrambling, the latter decreasing with pressure, were observed. The sum of the quantum yields of the two processes is unity. Acetylene was formed with quantum yields of (5.6 ± 0.5) × 10 −3 at 3 torr and (1.5 ± 0.1) × 10 −3 at 13.5 torr. Isomerization and decomposition reactions are interpreted as consequences of the formation of triplet ethylene molecules in the quenching process. A modified mechanism for these reactions initiated by mercury,cadmium, and organic photosensitizers is proposed.