CO adsorption on the calcite(10.4) surface: a combined experimental and theoretical study

Area of Science:

• Surface Science
• Materials Chemistry
• Physical Chemistry

Background:

• Calcite surfaces are crucial in various geological and chemical processes.
• Understanding molecular interactions on calcite is key to controlling surface properties.
• Previous experimental data on CO adsorption on calcite surfaces are limited.

Purpose of the Study:

• To characterize the structural, chemical, and physical properties of natural cleaved (10.4) calcite surfaces.
• To determine the adsorption site, binding energy, and vibrational behavior of carbon monoxide (CO) on calcite.
• To provide experimental data and theoretical insights into CO-calcite interactions.

Main Methods:

• Combined non-contact atomic force microscopy (NC-AFM) and polarization-resolved infrared reflection absorption spectroscopy (IRRAS).
• Utilized carbon monoxide (CO) as a probe molecule under ultrahigh vacuum (UHV) conditions.
• Employed density functional theory (DFT) calculations for data interpretation.

Main Results:

• Identified a single CO adsorption site on the well-defined cleaved calcite (10.4) surface.
• Observed a blue-shifted C-O vibrational band at 2175.8 cm⁻¹ at low CO exposure, shifting to 2173.4 cm⁻¹ at full monolayer coverage.
• Determined a CO binding energy of -0.31 eV and found CO prefers adsorption on calcium in a tilted orientation.
• NC-AFM imaged single CO molecules as depressions on surface features.

Conclusions:

• The cleaved calcite (10.4) surface is structurally well-defined, featuring a single primary CO adsorption site.
• CO adsorption on calcite exhibits coverage-dependent frequency shifts and repulsive adsorbate-adsorbate interactions.
• The study provides a comprehensive understanding of CO-calcite surface interactions, aided by DFT calculations.