SIMS and TDS study of the reaction of water and oxygen on Pt(111)

The reaction of H₂¹⁶O with ¹⁸O on Pt(111) was investigated using temperature programmed static secondary ion mass spectrometry (TPSSIMS), SSIMS and thermal desorption spectroscopy (TDS). The TPSSIMS behavior of the H₃O⁺ and H₃¹⁸O⁺ signals, after coadsorption of the reactants at 95 K, indicates that the isotopic exchange rate increases sharply at temperatures above 130 K. At 150 K, hydroxyl formation is indicated by a sharp drop in the H₃O⁺ and a similar sharp increase in the H₃¹⁸O⁺ signals. Using TDS, the overall stoichiometry of the reaction was determined to be 2H₂O(a)+O(a)→ 3 OH(a)+H(a). SSIMS data suggest that at least two kinds of hydroxyls are formed and that they do not interconvert at 160 K.