Infrared-visible sum-frequency generation was used to obtain vibrational spectra of hydrogen on C(111). From a fully relaxed (1×1) surface, a single sharp peak at ∼2830 ${\mathrm{cm}}^{\mathrm{-}1}$ was observed, which can be identified as the CH stretch mode from H on top sites. With the surface freshly transformed from (2×1) to (1×1), however, another peak at a higher frequency was detected. This is attributed to H adsorbed on a metastable (1×1) structure.

• Received 15 August 1991

DOI:https://doi.org/10.1103/PhysRevB.45.1522