Influence of Dipole–Dipole Interactions on Coverage-Dependent Adsorption: CO and NO on Pt(111)

Abstract

Density functional theory (DFT) calculations of energetic, geometric, vibrational, and electrostatic properties of different arrangements of CO and NO at quarter and half monolayer coverage on Pt(111) are presented. Differences in the extents of electron back-donation from the Pt surface to these molecules cause the low-coverage adsorbate dipoles to have opposite signs at atop and more highly coordinated bridge or fcc sites. These dipoles of opposite sign occupy adjacent positions in the experimentally observed atop-bridge or atop-fcc high -coverage arrangements, leading to attractive electrostatic interactions and concomitant changes in dipole moments, bond lengths, and vibrational frequencies. The interaction energies are estimated by charge partitioning to extract individual dipoles from the mixed arrangement and by calculations of field-dipole interactions. These estimated dipole interactions contribute significantly (20-60%) to the DFT-calculated relative stability of mixed arrangements over atop-, bridge-, or fcc-only arrangements and thus play an important role in coverage-dependent adsorption. We further extend these analyses to a range of molecules with varying dipole moments and show that the general nature of these interactions is not limited to CO and NO.

Coverage dependent non-adiabaticity of CO on a copper surface

“…49 They are mediated by adsorbate-induced modification of the local electron density 50,51 or by dipole-dipole interactions. 52 Recent theoretical work, using improved potential energy surfaces, revealed that the angular degrees of freedom of CO on copper play an important role in energy redistribution between vibrational states. 53 Nearby adsorbates could easily influence these angular states.…”

First-principles Thermodynamic Models in Heterogeneous Catalysis

“…9 Adsorbates in close proximity tend to interact, leading to coverage-dependent binding energies, 8,[10][11][12] and activation energies sensitive to co-adsorbates. 13 Through-surface electronic effects, 14 surface strain, 12 and through-space electrostatics 15 are but a few of the many mechanisms by which adsorbates can interact.…”

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

“…This behavior could be explained by different local dipole moments of CO at the two different adsorption sites 19 . Later calculations showed that the dipole moment of CO has indeed opposite sign when adsorbed on the bridge site as compared to the atop site 23 . It is known that the small dipole moment of CO depends on the strength of the bonding to a metal surface, 24 and a change of adsorption site could lead to the observed change of polarity.…”