Methyl on Cu(111)––structural determination including influence of co-adsorbed iodine

The adsorption geometry of the methyl species on Cu(111) with and without coadsorbed iodine has been determined using scanned energy mode photoelectron diffraction. Under all circumstances the three-fold-coordinated hollow sites are occupied. At saturation coverage of pure methyl species only the `fcc' site, directly above a third layer Cu atom is occupied, whereas at half saturation coverage ∼70% of the methyl species occupy these fcc hollows and ∼30% occupy the `hcp' sites above second layer Cu atoms. Best agreement between theory and experiment corresponded to a methyl group adsorbed with C3v symmetry, but the possibility that the species was tilted on the surface could not be excluded. The height of the C above the surface in a pure methyl layer was 1.66±0.02 Å, but was reduced to 1.62±0.02 Å in the presence of co-adsorbed iodine, suggesting that iodine may increase the strength of adsorption. Iodine was also found to occupy the fcc hollow sites with a Cu–I bondlength of 2.61±0.02 Å.