Short-Range Catalyst-Surface Interactions Revealed by Heterodyne Two-Dimensional Sum Frequency Generation...

Area of Science:

• Surface Science
• Spectroscopy
• Catalysis

Background:

• Understanding adsorbate-substrate interactions is key for designing efficient catalysts.
• Vibrational spectroscopy can probe molecular behavior at surfaces, but distinguishing surface effects is challenging.

Purpose of the Study:

• To investigate the influence of short-range surface interactions on the vibrational spectra of a model CO2 reduction catalyst.
• To establish a method for determining molecular orientation on surfaces using vibrational spectroscopy.

Main Methods:

• Employed Heterodyne 2D sum frequency generation (HD 2D SFG) spectroscopy.
• Studied a rhenium complex, Re(diCN-bpy)(CO)3Cl, as a monolayer on a gold surface.
• Analyzed line-shape differences and polarization dependences of infrared (IR) spectra.

Main Results:

• Observed significant line-shape differences in vibrational bands due to short-range molecule-surface interactions.
• Attributed these differences to couplings between CO vibrational modes and gold surface image dipoles.
• Successfully determined the ensemble-averaged orientation of the catalyst molecules on the gold surface.

Conclusions:

• HD 2D SFG spectroscopy is highly sensitive to short-range adsorbate-substrate interactions.
• This technique provides an unambiguous method for determining molecular orientation on surfaces.
• The findings are applicable to a wide range of adsorbate-substrate systems for surface characterization.