Abstract Chemisorption of methanol on polycrystalline magnesium is studied by time-of-flight analysis of directly recoiled (DR) surface atoms, angular resolved X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The combined measurements show that decomposition occurs to form ∼ 0.14 monolayers of surface hydroxide at methanol exposures < 4 L. High exposures result in molecular chemisorption to form a single methoxide overlayer. The DR results reveal that the C and H of the methyl group are the outermost atoms on the saturated surface. Analysis of DR intensities allows calibration of the relative signals and comparison with calculated recoil cross sections. The methoxide/Mg system provides a standard for surface hydrogen concentrations by the direct recoil technique.