Transient CO desorption from thin Pt films induced by mid-IR pumping

Area of Science:

• Surface Science
• Physical Chemistry
• Spectroscopy

Background:

• Understanding the dynamics of molecules adsorbed on metal surfaces is crucial for catalysis and materials science.
• Investigating vibrational relaxation and desorption mechanisms provides insights into surface-molecule interactions.
• Thin metal films offer unique properties for surface studies due to their high surface area to volume ratio.

Purpose of the Study:

• To investigate the vibrational dynamics of carbon monoxide (CO) adsorbed on heterogeneous platinum (Pt) layers of varying thicknesses (0.2 nm, 2 nm, 10 nm) in an aqueous solution.
• To differentiate between vibrational relaxation and desorption pathways using resonant and off-resonant pump-probe spectroscopy.
• To elucidate the mechanism of CO desorption induced by mid-infrared laser pulses.

Main Methods:

• Utilized resonant and off-resonant mid-infrared pump-probe spectroscopy.
• Studied CO adsorbed on thin (0.2 nm, 2 nm, 10 nm) heterogeneous Pt layers in an aqueous environment.
• Analyzed transient spectroscopic signals to determine vibrational lifetimes and desorption characteristics.

Main Results:

• Observed vibrational relaxation of the CO internal stretch vibration with a lifetime of approximately 3 picoseconds (ps) under resonant pumping.
• Off-resonant pumping revealed signals attributed to Pt layer heating and transient CO desorption.
• Confirmed that CO desorption is a thermal process, dependent on absorbed light fluence rather than wavelength.
• Demonstrated that thin Pt layers enhance CO desorption by concentrating absorbed energy.

Conclusions:

• Thin platinum layers effectively promote thermal desorption of adsorbed CO molecules in aqueous solutions.
• Vibrational dynamics, specifically relaxation, occur on a picosecond timescale.
• Pump-probe spectroscopy is a valuable tool for distinguishing vibrational relaxation from light-induced desorption processes.