ADSORPTION OF K AND COADSORPTION OF K AND C6D6 ON RH(111)

Alkali coadsorption is known to promote adsorption and reaction in certain cases. Alkali atoms act as electron donors to the metal and thus influence the molecule-metal interaction in a specific way. In a first step we investigated the adsorption of potassium on Rh(111) as a function of temperature and coverage with angle-resolved photoelectron spectroscopy (ARUPS) using synchrotron radiation of the storage ring at Berlin (BESSY). In a next step we concentrate on benzene adsorption on a Rh(111) surface where a new pure benzene structure (square-root 19 x square-root 19)R23.4-degrees was observed. The relative coverage can be determined to theta-C6H6 = 0.159 with 3 C6D6 molecules in the unit cell as deduced from CO coadsorption experiments. The coadsorption of K with C6D6 on Rh(111) has also been investigated by low-energy electron diffraction (LEED). At an elevated temperature (T = 320 K) demixing into separate C6D6 and K phases has been observed.