ANOMALIES IN SURFACE KINETICS CAUSED BY ISOTOPE DEPENDENT COMPRESSION AND PHONON STIFFENING OF MOLECULAR-HYDROGEN MONOLAYERS ON A TRANSITION-METAL SURFACE

We have investigated the layerwise growth and the coverage-dependent sticking coefficients of H2 and D2 on the (1×1)H/Ru(001) surface at ∼5 K by precise thermal desorption spectrometry. Strong compression of the first layer compared to the higher ones (by 22% for H2, 12% for D2) is observed. Desorption energies and sticking coefficients drop precipitously in the compression range. We explain all these effects by the large, mass-dependent zero-point widths of these molecules in the layers, with consequent high compressibilities and stiffening-induced decrease of collisional energy transfer. © 1995 The American Physical Society.