The chemistry of C 2 perfluoroalkyl iodide on the Cu(1 1 1) single crystal surface

Abstract

The thermal chemistry of perfluoroethyl iodide (C 2F 5I) adsorbed on Cu(1 1 1) has been investigated by temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). I 4d and F 1s XPS spectra show that dissociative adsorption of C 2F 5I to form the surface-bound perfluroethyl (Cu–C 2F 5) moieties occurs at very low temperature ( T < 90 K), while the C–F bond cleavage in adsorbed perfluroethyl (Cu–C 2F 5) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of βCF 3 αCF 2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (⩾0.16 L exposure), the adsorbed perfluroethyl (Cu–C 2F 5) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (Cu CF–CF 3) followed by a dimerization step to form octafluoro-2-butene (CF 3CF CFCF 3) at 315 K as gas product. The surface-bound (Cu–C 2F 5) decomposes preferentially, at low coverages (⩽0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (Cu CCF 3), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF 3C CCF 3) at 425 K. However, at middle coverages (ca. 0.08–0.16 L exposure), the adsorbed perfluroethyl (Cu–C 2F 5) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu–CF 2–CF Cu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF 2CFCFCF 2) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF 3CF CFCF 3 and CF 3C CCF 3, obey first-order kinetics, whereas the formation of CF 2CFCFCF 2 follows second-order kinetics.