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Collision-Induced Migration of Adsorbates on Solid Surfaces: An Experimental Approach I. M. Danziger and M. Asscher*

Summary: Collision-Induced Migration of Adsorbates on Solid Surfaces: An Experimental Approach
I. M. Danziger and M. Asscher*
Department of Physical Chemistry and the Farkas Center for Light Induced Processes,
The Hebrew UniVersity of Jerusalem, Jerusalem 91904, Israel
ReceiVed: NoVember 24, 2005; In Final Form: March 19, 2006
Collision-induced migration (CIM) is a process in which energetic gas-phase atoms or molecules at the tail
of the Boltzmann distribution enhance surface migration of adsorbates upon collision. It is believed to exist
and play an important role in any realistic high pressure-high-temperature heterogeneous catalytic system.
Combining supersonic beam-surface collision setup with in-situ optical second harmonic generation diffraction
technique from a coverage grating, we have shown, for the first time, that indeed energetic collisions (Kr
seeded in He) promote surface mobility of CO-K surface complex on Ru(001) with a threshold total kinetic
energy of 3 eV. An average migration distance/collision of more than 30 adsorption sites was estimated from
the experimental data at Kr total energy of 3.8 eV. This long-range migration distance per collision is understood
in terms of a cascade migration mechanism, where adsorbed CO molecules collide and push their neighbors
from high to low coverage areas, in a direction dictated by the collision momentum vector. A similar mechanism
has recently been suggested to explain adsorbate mobility at high coverage induced by an STM tip.
1. Introduction
Diffusion of adsorbates is among those primary processes
on solid surfaces that govern heterogeneous catalysis via
Langmuir-Hinshelwood mechanism. In addition it dictates the


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


Collections: Chemistry