The adsorption and reactions of HOCH2CH2NH2 on oxygen-precovered Cu(100) were investigated under ultrahigh vacuum conditions. Reflection–absorption infrared spectroscopy (RAIRS) studies were performed to monitor and identify the surface intermediates from HOCH2CH2NH2 decomposition, with the assistance of density functional theory (DFT) calculations. −OCH2CH2NH− was generated from scission of both the O−H and N−H bonds of HOCH2CH2NH2 and decomposed to form surface −OCH2CH2N− and to evolve CH2O and HCN observed with temperature-programmed reaction/desorption (TPR/D). The −OCH2CH2N− species further decomposed to generate H2, HCN, and N2, together with surface carbon. The bonding structures of the two surface intermediates, −OCH2CH2NH− and −OCH2CH2N−, were also investigated by DFT calculations.

Monitoring surface species and their bonding structures in link to specific chemical processes has long been an active, important subject in heterogeneous catalysis. In this article, with employment of temperature-programmed reaction/desorption, reflection− absorption infrared spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy in combination with density functional theory computation, we present three CH 3 CN formation channels from reaction of CH 2 CN generated by ICH 2 CN dissociative adsorption on Cu(100) and first spectroscopic evidence for CHCN on single crystal surfaces. The CH 3 CN formation mechanisms are dependent on CH 2 CN adsorption geometries. At lower coverages, CH 2 CN is adsorbed with the C−C−N approximately parallel to the surface. Reaction of these adsorbates produces CH 3 CN via firstand second-order kinetics, with the largest desorption rates occurring at 213 K and ∼400 K, respectively. At or near a saturated first-layer coverage, decomposition of ICH 2 CN forms C-bonded CH 2 CN (−CH 2 CN), which then transforms to N-bonded −NCCH 2 with tilted orientation. Disproportionation of the −NCCH 2 generates CH 3 CN at ∼324 K. Thermal products of H 2 , HCN and (CN) 2 evolving at higher temperatures are originated from the CHCN dissociation. On oxygen-precovered Cu(100), reaction of CH 2 CN forms new surface intermediates of vertical −NCO and −CCO, in addition to perturbed CH 3 CN desorption. In the conditions studied, formation of H 2 , HCN, and (CN) 2 is terminated due to the presence of preadsorbed O. −NCO and −CCO on O/Cu dissociate at ∼525 and 610 K, respectively, into CO and CO 2 .

The chemistry of 2-iodoacetic acid on Cu(100) has been studied by a combination of reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reaction/desorption (TPR/D), and theoretical calculations based on density functional theory for the optimized intermediate structures. In the thermal decomposition of ICH(2)COOH on Cu(100) with a coverage less than a half monolayer, three surface intermediates, CH(2)COO, CH(3)COO, and CCOH, are generated and characterized spectroscopically. Based on their different thermal stabilities, the reaction pathways of ICH(2)COOH on Cu(100) at temperatures higher than 230 K are established to be ICH(2)COOH --> CH(2)COO + H + I, CH(2)COO + H --> CH(3)COO, and CH(3)COO --> CCOH. Theoretical calculations suggest that the surface CH(2)COO has the skeletal plane, with delocalized pi electrons, approximately parallel to the surface. The calculated Mulliken charges agree with the detected binding energies for the two carbon atoms in CH(2)COO on Cu(100). The CCOH derived from CH(3)COO decomposition has a CC stretching frequency at 2025 cm(-1), reflecting its triple-bond character which is consistent with the calculated CCOH structure on Cu(100). Theoretically, CCOH at the bridge and hollow sites has a similar stability and is adsorbed with the molecular axis approximately perpendicular to the surface. The TPR/D study has shown the evolution of the products of H(2), CH(4), H(2)O, CO, CO(2), CH(2)CO, and CH(3)COOH from CH(3)COO decomposition between 500 and 600 K and the formation of H(2) and CO from CCOH between 600 and 700 K. However, at a coverage near one monolayer, the major species formed at 230 and 320 K are proposed to be ICH(2)COO and CH(3)COO. CH(3)COO becomes the only species present on the surface at 400 K. That is, there are two reaction pathways of ICH(2)COOH --> ICH(2)COO + H and ICH(2)COO + H --> CH(3)COO + I (possibly via CH(2)COO), which are different from those observed at lower coverages. Because the C-I bond dissociation of iodoethane on copper single crystal surfaces occurs at approximately 120 K and that the deprotonation of CH(3)COOH on Cu(100) occurs at approximately 220 K, the preferential COOH dehydrogenation of monolayer ICH(2)COOH is an interesting result, possibly due to electronic and/or steric effects.

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.

Temperature-programmed reaction/desorption (TPR/D) and reflection−absorption infrared spectroscopy (RAIRS) have been employed to study the reactions of CH 2  CHBr and CH 3 CHBr 2 on Cu(100) and O/Cu(100). In the TPR/D study, CH 2 CHCHCH 2 is the sole product detected from the reaction of CH 2 CHBr adsorbed on Cu(100) and featured by complex, coverage-dependent thermal desorption profiles (∼220−380 K). The preadsorbed oxygen can modify the evolution behavior of 1,3-butadiene from the CH 2 CHBr reaction but has no influence on the main 1,3-butadiene formation at 265 K. Moreover, the surface oxygen participates in the CH 2 CHBr reaction, forming an intermediate of >CCO, as well as additional products of H 2 O, C 2 H 2 , CO, and CO 2 , presumably via H-abstraction. New reaction pathways, which are otherwise not observed in the TPR/D study, are opened when CH 2 CHBr impinges on Cu(100) at high temperatures. At 500 K, H 2 , C 2 H 2 , and C 2 H 4 are generated from the incident CH 2 CHBr molecules upon Cu(100). The reaction of adsorbed CH 3 CHBr 2 on Cu(100) only forms CH 3 CHCHCH 3 in TPR/D experiments. This product can be generated at the surface temperature as low as 120 K. Preadsorbed oxygen on Cu(100) can increase the 2-butene formation to 190 K, the peak temperature. An additional product of CH 3 CHO is also formed, but its amount is small. Apparently, preadsorbed oxygen on Cu(100) has different effects on the reaction pathways for the adsorbed CH 2 CHBr and CH 3 CHBr 2 .