ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
We report a first computation of the geometry of HBr adsorbed on a LiF(001) substrate. The interaction energy of 200 HBr molecules with periodic boundary conditions was determined with respect to adsorbate–substrate and adsorbate–adsorbate electrostatic interaction (point charges in HBr simulated its dipole and multipoles) as well as a short-range "core'' potential (comprising dispersion forces and repulsive overlap). The monolayer heat of adsorption at T=100 K according to this model was 0. 27 eV, which was also the experimental value [E. B. D. Bourdon, et al., J. Chem. Phys. (submitted)]. The major contribution to this energy came from electrostatic binding. The preferred HBr location at all surface coverages (0.25, 0.50, and 1.0 ML) in the temperature range T=70–130 K was with Br over Li+ and H almost eclipsing one of the four neighboring F−. In this configuration, Br–H is tilted down by 23 ° from the crystal plane in an arrangement resembling a Br–H– –F− hydrogen bond. This computed geometry agrees well with recent experimental findings for HBr/LiF(001) using polarized infrared spectroscopy [P. M. Blass et al.; J. Chem. Phys. (submitted)], and is also in qualitative accord with the observed angular distribution of fast H from the photolysis of HBr adsorbed on LiF(001). At the separations dictated by the LiF(001) lattice, the net adsorbate–adsorbate interaction is attractive, leading to a tentative prediction of island formation at lower coverages under equilibrium conditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.459937
Permalink
