High Resolution Electron Energy Loss Spectroscopy of CO Co-Adsorbed with Cyanogen(C2N2) on Pt(111): Dielectric Screening of Dipole Scattered Modes

摘要

We have investigated the effects of the co-adsorption of CO with cyanogen on thevibrational spectrum of the CO as determined by high resolution electron energy loss spectroscopy. Since cyanogen is easily polarizable (polarizability approximately 53A3), we expected that the intensities of the CO vibrational spectra would be substantially modified by dipole screening effects. The linear CO stretching mode of on-top bonded CO is strongly screened by co-adsorbed C2N2. However, the CO stretching mode of bridge bonded CO is not strongly effected. The effect which we observe for on-top bonded CO is consistent with a dipole screening mechanism with a polarizability for the co-adsorbed C2N2 of approximately 41 A3 in reasonable agreement with the known polarizability Of C2N2. It is known that cyanogen adsorbs on Pt(l 1 1) in two bonding states referred to in the literature as the a-state, and the B-state of cyanogen. The dipole screening of the CO vibrations is entirely due to the (X-state of the coadsorbed cyanogen. Vibrational spectroscopy, HREELS, dipole screening, platinum, CO, C2N2.