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 of ClCH2CH2Cl on Cu(100) and O/Cu(100) in the subjects of identification of the rotational isomers, adsorption energy, adsorption geometry, thermal stability of the layer structure, and transformation between the trans and gauche conformers. On Cu(100), both the trans and gauche forms of ClCH2CH2Cl coexist on the surface at a monolayer coverage, and their thermal desorption peak appears at 187 K. The trans molecules are likely adsorbed with the C−Cl bonds approximately parallel to the surface. On O/Cu(100), the gauche conformer is the predominant species and the desorption temperature is shifted to 199 K. It is found that the ClCH2CH2Cl layer structure on Cu(100), up to a ∼15 monolayer coverage studied, is stable between 120∼140 K. However, O/Cu(100) shows an interesting contrast. The thermal stability only appears at a coverage below ∼3 monolayers. The transformation from gauche to trans takes place for higher coverages. On the basis of the cluster-model calculations without consideration of the interaction between adsorbed molecules, it is shown that the activation energy for the transformation between trans and gauche ClCH2CH2Cl on O/Cu(100) is much lower than that on Cu(100), suggesting that the trans molecules are easier to be transformed into gauche ones on O/Cu(100), as they are adsorbed on the proximity of preadsorbed oxygen atoms.

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X-ray photoelectron spectroscopy has been employed to study the surface intermediates from the thermal decomposition of HSCH2CH2OH on Cu(111) at elevated temperatures. On the basis of the changes of the core-level binding energies of C, O, and S as a function of temperature, it is found that HSCH2CH2OH decomposes sequentially to form -SCH2CH2OH and -SCH2CH2O-. Theoretical calculations based on density functional theory for an unreconstructed one-layer copper surface suggest that -SCH2CH2OH is preferentially bonded at a 3-fold hollow site, with an adsorption energy lower than the cases at bridging and atop sites by 15.6 and 47.5 kcal x mol(-1), respectively. Other structural characteristics for the energy-optimized geometry includes the tilted C-S bond (14.1 degrees with respect to the surface normal), the C-C bond titled toward a bridging site, and the C-O bond pointed toward the surface. In the case of -SCH2CH2O- on Cu(111), the calculations suggest that the most probable geometry of the adsorbate has its S and O bonded at hollow and bridging sites, respectively. With respect to the surface normal, the angles of the S-C and O-C are 27.9 and 34.0 degrees.