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(a), which further decomposes to evolve FCH2CHO(g) at temperatures higher than ∼350 K. The decomposition of FCH2CH2OH to form FCH2CH2O(a) on oxidized Cu(100) begins at ∼160 K and is completed by 220 K. On clean Cu(100), FCH2CH2OH 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.

The reactions of BrCH 2 CH 2 OH were investigated on clean and oxygen-precovered Cu(100) surfaces under ultrahigh vacuum conditions. Reflection-absorption infrared spectroscopy (RAIRS) studies were performed to examine the surface intermediates that were generated from BrCH 2 CH 2 OH decomposition. Density functional theory calculations were employed to predict the infrared spectra, assisting in the identification of the reaction intermediates. On Cu(100), -CH 2 CH 2 O-, formed from the simultaneous scission of the bromine-carbon and oxygen-hydrogen bonds of BrCH 2 CH 2 OH at ∼190 K, decomposed and evolved into C 2 H 4 between 210 and 310 K in temperature-programmed reaction/desorption (TPR/D) experiments. A small amount of CH 3 CHO desorption was also observed. On oxygen-precovered Cu(100), -CH 2 CH 2 O-was also generated at lower exposures (<1.5 L) but at the BrCH 2 CH 2 OH dosing temperature of 115 K. The TPR/D study showed that C 2 H 4 with minor amounts of CH 3 CHO evolved between 210 and 310 K. However, at higher BrCH 2 CH 2 OH exposures (g1.5 L), BrCH 2 CH 2 O-was the major intermediate formed at ∼200 K. The formation temperature of C 2 H 4 and CH 3 CHO was extended to ∼400 K in this case.

Temperature-programmed reaction/desorption, reflection-absorption infrared spectroscopy, and density functional theory calculations have been employed to investigate the adsorption and thermal reactions of ClCH2CH2OH on clean and oxygen-precovered Cu(100) surfaces. On Cu(100), ClCH2CH2OH is mainly adsorbed reversibly. The ClCH2CH2OH molecules at a submonolayer coverage can change their orientation with increasing temperature. However, on oxygen-precovered Cu(100), all of the adsorbed ClCH2CH2OH molecules below 0.5 langmuir exposures completely dissociate to generate ethylene and acetaldehyde via the intermediate of ClCH2CH2O-. The computational studies predict that the ClCH2CH2O- is most likely to be adsorbed at the 4-fold hollow sites of Cu(100), with its C-O bond only slightly titled away from the surface normal and with a gauche conformation with respect to the C-C bond. The hollow-site ClCH2CH2O- has an adsorption energy that is 4.4 and 19.2 kcal x mol(-1) lower than that of the ClCH2CH2O- bonded at the bridging and atop sites, respectively. No significant effect of precovered oxygen on the ClCH2CH2O- bonding geometry and infrared band frequencies has been observed, as compared with the case without oxygen.