We have investigated the layerwise growth and the coverage-dependent sticking coefficients of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ 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 ${\mathrm{H}}_2$, 12% for ${\mathrm{D}}_2$) 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.

• Received 7 July 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.1147