Photodissociation dynamics of allene at 157 nm

Abstract

The photodissociation dynamics of allene at 157 nm have been investigated using photofragment translational spectroscopy (PTS). Detection of the H and H₂ photoproducts, along with their heavy partner fragments, allows an accurate assessment of the dynamics of the main photochemical processes. Three major channels have been identified: C–H bond fission, H₂ elimination, and methylene formation (CH₂+C₂H₂). The translational energy distribution of the C–H bond fission process indicates that there is little or no reverse barrier for the dissociation pathway and that the dissociation is rather statistical in nature. The translational energy distribution for the H₂ elimination processes is peaked at ∽18 kcal mol⁻¹, and covers a broad range in energy, indicating that there is a sizable reverse barrier for this process, which is typical of molecular hydrogen elimination in hydrocarbon molecules. The translational energy distribution for the CH₂ formation process is peaked at ∽8 kcal mol⁻¹, and also covers a wide range of energy, indicating that the process likely has a small reverse barrier. The relative yields for the H, H₂ and CH₂ formation processes are determined to be 1: 0.15:0.27.