No abstract

1,3-Thiazole is found to be nearly perpendicularly adsorbed on Cu(100), with the N atom attaching to an atop site and an adsorption energy of ∼19.5 kcal•mol −1 . The N−C−S moiety of the adsorbed 1,3-thiazole has a larger change in bond length as compared to a free 1,3-thiazole molecule. The adsorbed 1,3-thiazole can decompose below 200 K, forming atomic S and −CHCHNCH−. A small amount of R−S− (R: CHCHNCH) is detected on the surface at 200 K. Complete desulfurization of the 1,3-thiazole occurs at 400 K. Further reaction of the −CHCHNCH− produces H 2 and HCN at higher temperatures. In the presence of adsorbed oxygen atoms(O/Cu(100)), new disulfide intermediates (R−S−S−R, R: CHCHNCH) from the thiazole reaction are measured at 300 K and can further decompose into atomic S and −CHCHNCH− at 400 K. In addition, other surface species of −NCO and >CCO are also observed at 500 K. These species eventually react to generate H 2 O, CO, CO 2 , and N 2 . Further calculations indicate that the S−CHN bond of 1,3thiazole would break preferentially, as compared to the S−CHCH bond, in the decomposition process on Cu(100).

X-ray photoelectron spectroscopy, reflection–absorption infrared spectroscopy, temperature-programmed reaction/desorption, and density functional theory calculations have been performed to investigate the reaction mechanisms and bonding structures of 3- and 2-bromopropanoic acids on Cu(100) and oxygen-precovered Cu(100). On Cu(100), the bond dissociation of C–Br and O–H in BrCH2CH2COOH is accelerated, occurring at 110 K, as compared to the monofunctional molecules. CH2CH2COOH, CH2CH2COO, and CH3CH2COO from the BrCH2CH2COOH reaction coexist on Cu(100) at 180 K. The CH2CH2COOH is not detected at 250 K, and CH3CH2COO predominates at 320 K. The CH2CH2COO is strongly bonded to the surface via the COO and terminal CH2 groups. In the presence of oxygen atoms on Cu(100), the C–Br scission is suppressed and BrCH2CH2COO is found to be predominant at 150 K. CH2CH2COO begins to form at 200 K and further reacts to produce CH3CH2COO and CH2CHCOO at 320 K through disproportionation or sequential H loss at 2CH2 and hydrogenation at 3CH2. The reaction of CH3CHBrCOOH on Cu(100) also generates CH3CH2COO at 300 K via CH3CHCOOH and CH3CHCOO. The latter species could attach to the surface via the CHCOO or COO group. On O/Cu(100), dissociation of CH3CHBrCOOH forms CH3CHCOO between 200 and 400 K. CH3CHCOO on O/Cu(100) dehydrogenates, at 450 K, into CH2CHCOO. A halogen (Cl and Br) effect is observed in the adsorption structure and reaction path of CH3CHCOO on O/Cu(100).