ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Monte Carlo simulations have been carried out to study the adsorption structure of methyl halide molecules (CH3I and CH3Br) on a LiF(001) surface. The ionic substrate is treated as a three-dimensional stationary mesh of point charges and the adsorbed molecules are taken as rigid bodies. The adsorption at different coverages in the monolayer and submonolayer regimes is investigated. The interaction potential between the surface and adsorbate includes electrostatic contributions due to ion–dipole (both permanent and induced) interactions and Lennard-Jones terms that are introduced to account for the remaining interactions. The adsorbate–adsorbate interaction is assumed to be the sum of the permanent dipole–dipole and Lennard-Jones potentials. All the interaction potentials are assumed to be pairwise. The adsorbate–adsorbate interaction is dominated by the Lennard-Jones component, largely due to the halogen–halogen interaction, while Coulomb forces account for a few percent of the total adsorption energy. As a result, the adsorbates tend to form close-packed structures on the surface. The optimal adsorbate structure on the surface is determined by the relative strength of the adsorbate–adsorbate vs adsorbate–substrate interactions. For high coverages close to monolayer, the system has the lowest energy when the molecular axes of the adsorbates are parallel to the surface normal with alternating methyl-up and methyl-down configurations. For an isolated molecule, however, the preferred orientation is perpendicular to the surface normal.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.464731
