Hydration of Co adsorbed on Pt(100) at cryogenic temperatures in UHV environments

Adsorption of small amounts of D ₂O (ca. 0.01 L exposure) on CO(sat)/Pt(100) surfaces in ultrahigh vacuum at 105 K was found to split the asymmetric peak at 2100 cm ^-1 in the infrared reflection absorption spectra attributed to the stretching of CO adsorbed on atop sites into two clearly defined features: an intense component, which shifted toward lower energies due to surface hydration of adsorbed CO (originally at 2100 cm ^-1, peak a), and a smaller peak centered at 2094 cm ^-1 (peak b), which remained fixed in position even after closing the D ₂O dosing valve. The energies of peaks a and b, as determined by statistical analyses, correlated very well with those reported in the literature for CO adsorbed at high coverages on Pt(100) originally in the (5 × 20) or (hex) reconstruction, and on the unreconstructed Pt(100)-(1 × 1), respectively, at 90 K. On these bases, the asymmetry of the peak observed for CO(sat)/Pt(100) (no D ₂O dosing) is ascribed to the presence of CO linearly adsorbed on these two different sites on the surface, for which the rate of hydration is larger for the (5 × 20) compared to the (1 × 1) phases.