Adsorption and reactions of ClCH₂CH₂OH on clean and oxygen-precovered Cu(100): Experimental and computational studies

Temperature-programmed reaction/desorption, reflection-absorption infrared spectroscopy, and density functional theory calculations have been employed to investigate the adsorption and thermal reactions of ClCH₂CH ₂OH on clean and oxygen-precovered Cu(100) surfaces. On Cu(100), ClCH₂CH₂OH is mainly adsorbed reversibly. The ClCH ₂CH₂OH 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·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.