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Formation and dynamics of water clusters on Ru,,001... Y. Lilach,a)

Summary: Formation and dynamics of water clusters on Ru,,001...
Y. Lilach,a)
V. Buch,b)
and M. Asscherc)
Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Received 18 February 2003; accepted 16 September 2003
The adsorption kinetics of water on Ru 001 was simulated using molecular dynamics MD and
equilibrium-model approach. The results nicely reproduce observations from STM imaging, work
function change, and IR measurements. The agreement with experimental results is based on the
formation of stable clusters already at very low surface coverage and temperature. Tetramers are
predicted to be relatively stable compared to smaller and larger clusters. The dipole moment per
water molecule continuously decreases from 2.2D for the monomer down to 1.1D for pentamer and
larger clusters. Dimers are found to diffuse faster than monomers or larger clusters, with activation
energy for diffusion of 2.9 kcal/mol, in agreement with recent STM measurements. A unique
mechanism for dimers diffusion is proposed. Temperature programmed desorption TPD spectra
from a metal surface were calculated by employing the MD scheme. These spectra were found
identical to the standard Redhead line-shape analysis of the experimental TPD spectra of water from
Pt 111 and Ru 001 , an observation that was used to verify the consistency of the MD procedure.
Finally, a kinetic model, fed by the MD calculated decreasing dipole moments per water molecule
at larger clusters, explains well the highly nonlinear initial stages up to 0.35BL of the work


Source: Asscher, Micha - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry