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, similar to20% 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(a), which further decomposes to evolve FCH2CHO(g) at temperatures higher than similar to350 K. The decomposition of FCH2CH2OH to form FCH2CH2O(a) on oxidized Cu(I 00) begins at similar to160 K and is completed by 220 K. On clean Cu(100), FCH2CH2OH molecules at similar to0.25 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.