Thermal Decomposition and Adsorption Orientation of 2-Fluoroethanol on Clean and Oxidized Cu(100)

Temperature-programmed reaction/desorption and reflection-absorption infrared spectroscopy have been employed to investigate the thermal reactions and adsorption geometry of FCH₂CH₂OH molecules on clean and oxygen-preadsorbed Cu(100) surfaces. Molecular desorption predominates in heating FCH₂CH₂OH adsorbed on clean Cu(100). However, ∼20% adsorbed FCH₂CH₂OH molecules at about half-monolayer coverage dissociate on the surface to form water, ethylene, and 1,4-dioxane. On the other hand, monolayer FCH₂CH₂OH completely dissociates on oxidized Cu(100) to form 1,4-dioxane and the surface intermediate of FCH₂CH₂O_(g), which further decomposes to evolve FCH₂CHO_(g) at temperatures higher than ∼350 K. The decomposition of FCH₂CH₂OH to form FCH₂CH₂O_(g) on oxidized Cu(100) begins at ∼ 160 K and is completed by 220 K. On clean Cu(100), FCH₂CH ₂OH molecules at ∼0.25 monolayer coverage are adsorbed with the C-C-O skeleton approximately parallel to the surface. The C-C-O skeleton tilts away from the surface as the exposure is increased to a half-monolayer coverage. However, the parallel C-C-O orientation is not observed on the oxidized surface, even at the FCH₂CH₂OH exposure for a 0.25 monolayer coverage.