Infrared absorption measurement of the overtone of the wagging mode of hydrogen on W(100).

The infrared absorption of H chemisorbed on W(100) has been studied as a function of coverage. We find that, in addition to the fundamental symmetric stretch absorption, the overtone absorption of the wagging mode can also be measured as the coverage approaches saturation. These assignments are confirmed by isotopic mixture experiments. The strong enhancements of the overtone absorption is correlated with the p(1x1) structure of the top W layer (unreconstructed) and is believed to result from a strong coupling of the wag motion to bands of surface states located at the Fermi level. This coupling provides an efficient vibrational decay mechanism through the production of electron-hole pairs.