Adsorption and reactions of propenoic acid and 2-fluoropropanoic acid on Cu(100) and O/Cu(100).

X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed reaction/desorption have been employed to investigate the adsorption and reaction pathways of CH₂=CHCOOH and CH₃CHFCOOH on Cu(100) and oxygen-precovered Cu(100) [O/Cu(100)]. In the case of CH₂=CHCOOH on O/Cu(100), CH₂=CHCOO is the surface intermediate detected between 110 K and 400 K. CH₂=CHCOO is adsorbed vertically and can change adsorption sites at a higher temperature. The propenoate (acrylate) decomposes at higher temperatures (>500 K), with formation of >C=C=O (ketenylidene) surface species and gaseous products. On Cu(100), CH₂=CHCOOH is adsorbed in dimer form and can dissociate to generate CH₂=CHCOO and CH₃CHCOO intermediates on the surface. The CH₃CHCOO continuously recombines with the H from deprotonation of CH₂=CHCOOH, resulting in the formation CH₃CH₂COO. The co-existing CH₂=CHCOO and CH₃CH₂COO further decompose at ∼550 K to evolve reaction products, but without >C=C=O being detected. On O/Cu(100), CH₃CHFCOOH readily deprotonates to form CH₃CHFCOO at 120 K. This intermediate reacts on the surface at ∼460 K to evolve gaseous products, also producing CH₂=CHCOO. In the case of Cu(100), deprotonation of CH₃CHFCOOH occurs at ∼250 K, forming CH₃CHFCOO. Without oxygen on the surface, this intermediate decomposes into HF and CH₂=CHCOO at ∼455 K. [ABSTRACT FROM AUTHOR]