Adsorption of a water molecule on Fe(100): Density-functional calculations

Abstract

Molecular and dissociative adsorption of a single water molecule on the Fe(100) surface has been studied by using density-functional theory calculations. We found that there exists a locally stable molecular adsorption state with an adsorption energy of 0.39 eV, where the H(2)O molecule adsorbs on top of a surface Fe atom in a flat-lying molecular configuration. This molecular configuration is found to well reproduce the water-induced vibrational frequencies measured in a low-temperature electron-energy-loss spectroscopy (EELS) study. The H(2)O molecular state is subject to a dissociation into H+OH species with an activation barrier of 0.35 eV. A further dissociation of the OH group into H+O species requires a higher activation energy of 0.79 eV. The prediction of the H(2)O molecular precursor and the energy diagram for its dissociation is in good accordance with the adsorption picture which was suggested in a previous EELS study but has been incompatible with a previous density-functional study predicting a barrierless H+OH dissociation of water molecule.