Photolysis of ethyl iodide at 77 K

Abstract

Detailed analytical studies of the 253.7 nm photolysis of films of pure C₂H₅I at 77 K establish that the initial photo-process leads exclusively to formation of C₂H₄ and HI with a quantum yield of 0.36. The quantum yield for ethyl radical formation is estimated as 5 × 10^–4 from a study of CF₃CH₂I photolysis and comparison with earlier work.² The formation of C₂H₆, I₂, n-C₄H₁₀ and H₂, the latter never previously detected, is shown to be entirely secondary in nature and the relative yields are time and C₂H₅I-concentration independent. Secondary photolysis involves the complex C₂H₅I · HI rather than free HI. A mechanism based on the photolysis of C₂H₅I aggregates and cage-formed complexes is proposed and the marked photo-inhibition observed as reaction proceeds is established to be a consequence of formation of the further complex, C₂H₅I · I₂· IH, for which a cyclic structure is proposed.