Adsorption of intact methanol on Ru(0001).

Fourier transform infrared absorption spectroscopy has been used to study the adsorption of methanol on the clean Ru(0001) surface at T<or=80 K. Thereby, clear evidence for intact adsorption has been found. This observation contradicts previous studies which suggested an OH (OD) bond scission upon adsorption of methanol on Ru(0001), even at low temperatures, as well as partial recombinative desorption at higher T. Our conclusion is based on isotopic shifts of vibrational modes associated with the OH (OD) group of adsorbed CH(3)OH and CH(3)OD. Density functional theory (B3LYP) confirms these findings, as it reproduces the observed frequencies and isotopic shifts well. Additional support for our conclusion of nondissociative adsorption of methanol on Ru(0001) is provided by thermal desorption experiments of CH(3)OH coadsorbed with deuterium on Ru(0001). We find that CH(3)OD formation is clearly below detection threshold, while desorption of CH(3)OH is quite prominent; a recombinative desorption of dissociated methanol and hydrogen/deuterium as suggested in the literature is therefore discarded. At very low coverages and temperatures the presence of isolated methanol molecules or dimers is suggested. With increasing density or by annealing a low coverage methanol layer, hydrogen bonding leads to cluster formation, as evidenced by an intensity loss of those vibrational modes affected by hydrogen bonds, in conjunction with a substantial line broadening.