Multimode vibrational activation and energy transfer in single-molecule CO hopping on Pd(111)

Area of Science:

• Surface science
• Chemical physics
• Nanotechnology

Background:

• Understanding molecular motion on surfaces is crucial for catalysis and nanotechnology.
• Vibrational energy transfer plays a key role in surface reactions, but mechanisms are complex.
• Previous studies have explored molecule-surface interactions, but specific vibrational activation pathways require further investigation.

Purpose of the Study:

• To investigate vibrationally induced single-molecule hopping of carbon monoxide (CO) on a Pd(111) surface.
• To identify vibrational thresholds and energy transfer mechanisms governing molecular motion.
• To compare reaction yields and mechanisms between different palladium surfaces (Pd(111) and Pd(110)).

Main Methods:

• Utilizing scanning tunneling microscope-based action spectroscopy (STM-AS) to probe molecular dynamics.
• Analyzing vibrational thresholds and correlating them with molecular vibrational modes (M-C stretch, C-O stretch).
• Employing Morse potential fitting to quantify anharmonicity and assess overtone-driven activation.

Main Results:

• Observed distinct vibrational thresholds for CO hopping at 96, 124, 142, and 230 meV.
• Identified these thresholds with high-order overtones of the M-C stretch and the fundamental C-O stretch modes.
• Demonstrated significantly higher hopping yields on Pd(111) compared to Pd(110) due to enhanced anharmonic coupling.

Conclusions:

• Vibrational overtones can effectively drive molecular motion (hopping) on metal surfaces.
• Anharmonic interactions are critical for efficient energy transfer and surface reaction dynamics.
• Site-dependent anharmonic coupling influences reaction yields, offering a pathway to control molecular motion at the atomic scale.