Compression and caging of CD3Cl by H2O layers on Ru(001)

Abstract

The interaction of two similar coadsorbed dipolar molecules H2O and CD3Cl has been studied as a function of coverage over Ru(001) under ultra high vacuum conditions. The complementary techniques of temperature-programmed desorption mass spectrometry (ΔP-TPD) and work function change in a Δφ-TPD mode were employed. Adsorption of water on top of CD3Cl reveals two major trends: At submonolayer methyl chloride coverage, post-deposited water compresses the methyl chloride molecules and forces them to flip over to the methyl down configuration at the second layer, leading eventually to three-dimensional islands. This is indicated by both CD3Cl ΔP-TPD and differential work function [d(Δφ)/dT] data. Higher water coverage [θ(H2O)>1.2 bilayers (BL)] causes full detachment of the CD3Cl molecules from the ruthenium surface, to be encapsulated within the amorphous solid water (ASW) layer that is formed. At even higher water coverage [θ(H2O)>5 BL], methyl chloride desorbs in an explosivelike mode at 165 K. The caged methyl chloride molecules lack any permanent dipole moment as indicated from differential Δφ-TPD analysis, explained in terms of a high level of disorder within the ASW. The relevance of the hydrophobic caging process to clathrate-hydrate formation is discussed.