The adsorption dynamics and geometry of phenylacetylene (PA) on Cu(100) was investigated by means of X-ray photoemission (XPS), near edge X-ray absorption (NEXAFS) spectroscopies and by quantum chemical calculations. The clean metal surface was exposed to PA vapors and the C1s core level spectrum evolution was monitored by means of time-resolved XPS measurements. Photoemission (C1s) and absorption (C K-edge) spectra were recorded both in monolayer and multilayer regimes; polarization-dependent NEXAFS investigations were carried out on the PA monolayer at room temperature (RT). The experimental results have been interpreted with the help of quantum chemical calculations: DFT (Density Functional Theory) plane-wave based calculations for the optimization of the interaction geometry of PA on a two layered (100)-slab of Cu atoms using periodic boundary conditions and ab-initio simulation of the XPS spectrum for a small cluster including PA in the optimized adsorbate geometry and the 2 Cu atoms more directly involved in the adsorption. Comparison between NEXAFS spectra of PA monolayer, adsorbed at room temperature and of PA multilayer condensed at 130 K, evidences a strong interaction taking place between the PA molecule and the Cu(100) surface. The modifications observed in the C1s->pi* region of the NEXAFS spectrum suggest, with the support of the theoretical results, the partial opening of the CC triple bond of the alkyn group, leading to a di-sigma-bond interaction with the metal substrate, while the structure of the benzene ring appears unaffected but undergoes torsion. The polarization dependence analysis of the pi* resonances intensity for PA monolayer, indicates that the normal to the benzene ring is tilted about 55 degrees with respect to the normal to the surface.
XPS, NEXAFS and theoretical study of phenylacetylene adsorbed on Cu(100)
V Carravetta;
2004
Abstract
The adsorption dynamics and geometry of phenylacetylene (PA) on Cu(100) was investigated by means of X-ray photoemission (XPS), near edge X-ray absorption (NEXAFS) spectroscopies and by quantum chemical calculations. The clean metal surface was exposed to PA vapors and the C1s core level spectrum evolution was monitored by means of time-resolved XPS measurements. Photoemission (C1s) and absorption (C K-edge) spectra were recorded both in monolayer and multilayer regimes; polarization-dependent NEXAFS investigations were carried out on the PA monolayer at room temperature (RT). The experimental results have been interpreted with the help of quantum chemical calculations: DFT (Density Functional Theory) plane-wave based calculations for the optimization of the interaction geometry of PA on a two layered (100)-slab of Cu atoms using periodic boundary conditions and ab-initio simulation of the XPS spectrum for a small cluster including PA in the optimized adsorbate geometry and the 2 Cu atoms more directly involved in the adsorption. Comparison between NEXAFS spectra of PA monolayer, adsorbed at room temperature and of PA multilayer condensed at 130 K, evidences a strong interaction taking place between the PA molecule and the Cu(100) surface. The modifications observed in the C1s->pi* region of the NEXAFS spectrum suggest, with the support of the theoretical results, the partial opening of the CC triple bond of the alkyn group, leading to a di-sigma-bond interaction with the metal substrate, while the structure of the benzene ring appears unaffected but undergoes torsion. The polarization dependence analysis of the pi* resonances intensity for PA monolayer, indicates that the normal to the benzene ring is tilted about 55 degrees with respect to the normal to the surface.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
