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Steric Effect in Electron-Molecule Interaction Yigal Lilach and Micha Asscher*

Summary: Steric Effect in Electron-Molecule Interaction
Yigal Lilach and Micha Asscher*
Department of Physical Chemistry and The Farkas Center for Light Induced Processes,
The Hebrew UniVersity, Jerusalem 91904, Israel
ReceiVed: October 21, 2003
A steric effect has been identified and measured in the interaction of electrons with oriented molecules, for
the first time. Photoelectron mediated reactivity has been determined, with a cross section of ) (3.0 ( 0.4)
(methyl down) for an adsorbed CD3Br on O/Ru(001). A three times smaller cross section was
obtained for the bromine down configuration, controlled by oxygen precoverage. A qualitatively similar
molecular orientation dependent effect was measured by direct bombardment with 10 eV electrons, however,
at much larger cross sections. The significance of the steric effect reported here for electron-transfer processes
in general is discussed.
Steric effects are among the oldest and most intuitive concepts
in chemical reactivity. Chemists have recognized very early that
proper mutual orientation of reactants is almost as important as
energetic requirements for a successful reactive encounter. One
experimental approach to study molecular orientation dependent


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


Collections: Chemistry