Surface infrared investigations of substrate electron - Hydrogen phonon coupling in Mo(100)-p(1x1)H and W(100)-p(1x1)H.

The surface infrared reflectance spectra of Mo(100)-p (1x1)H and W(100)-p(1x1)H are both characterized by two vibrational absorptions in the 800-4000 cm sup (-1) region - a broad band at 1016 cm sup (-1) at T = 100K for H on Mo(100) and at 1069 cm sup (-1) at T = 300K for H on W(100), corresponding to the symmetric stretch (v sub 1), and a narrow derivative-like feature at 1302 cm sup (-1) on Mo(100) and 1272 cm sup (-1) on W(100), identified as the first overtone of the wag motion (2v sub 2). The physical origin of the line shapes, as well as the larger intensity of the 2v sub 2 than expected from adiabatic considerations, were investigated through phenomenological line shape analysis of data obtained as a function of temperature, relative H/D and H/CO coadsorption concentrations. Dephasing processes, as opposed to surface inhomogeneities, contribute weakly to both v sub 1 and 2v sub 2 line widths. Strong effects due to H-H dynamic coupling are seen for v sub 1 on W(100)- p(1x1)H only.