Primary processes in the 121.6 nm photolysis of gas phase ethyl bromide

The vacuum UV photolysis of ethyl bromide at 121.6 nm (235.2 kcal mol⁻¹) has been studied over the pressure range 0.5 – 100 Torr at room temperature using a hydrogen atom resonance lamp. The scavenger effect of the reaction was observed by adding NO gas as a radical scavenger. The pressure effect was also investigated with CF₄ as an additive. The major products of the reaction were CH₄, C₂H₄, C₂H₆, C₂H₂ and CH₃CHBr₂ via a two-channel competition between molecular elimination and the formation of radicals. The decomposition modes in the primary process were 58.7% molecular elimination and 41.3% radical reaction. It was estimated that the portion of hot C₂H₄ molecules produced through the molecular elimination process with more than the threshold energy (E₀ = 80 kcal (mol⁻¹) for decomposition to C₂H₂ was 25% of the total energy distribution.