The chemistry of C2 perfluoroalkyl iodide on the Cu(1 1 1) single crystal surface

The thermal chemistry of perfluoroethyl iodide (C2F5I) 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 C2F5I to form the surface-bound perfluroethyl (Cu-C2F5) moieties occurs at very low temperature (T < 90 K), while the C-F bond cleavage in adsorbed perfluroethyl (Cu-C2F5) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of βCF3αCF2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (⩾0.16 L exposure), the adsorbed perfluroethyl (Cu-C2F5) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (CuCF-CF3) followed by a dimerization step to form octafluoro-2-butene (CF3CFCFCF3) at 315 K as gas product. The surface-bound (Cu-C2F5) decomposes preferentially, at low coverages (⩽0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (CuCCF3), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF3CCCF3) at 425 K. However, at middle coverages (ca. 0.08-0.16 L exposure), the adsorbed perfluroethyl (Cu-C2F5) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu-CF2-CFCu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF2CFCFCF2) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF3CFCFCF3 and CF3CCCF3, obey first-order kinetics, whereas the formation of CF2CFCFCF2 follows second-order kinetics.