Solvation Reaction Field at the Interface Measured by Vibrational Sum Frequency Generation Spectroscopy

Area of Science:

• Chemistry
• Materials Science
• Device Physics

Background:

• Interfacial electric fields are crucial but poorly understood due to measurement and modeling challenges.
• Existing models struggle with the asymmetric environment of conductor-dielectric interfaces.

Purpose of the Study:

• To experimentally investigate and theoretically model the interfacial electric field at a conductor-dielectric junction.
• To understand the influence of dielectric properties on molecular behavior at interfaces.

Main Methods:

• Utilized vibrational sum frequency generation (VSFG) spectroscopy to study the nitrile (CN) stretch of 4-mercaptobenzonitrile (4-MBN) on a gold surface.
• Developed an adapted Onsager reaction field model to account for the asymmetric metal-dielectric interface.

Main Results:

• Observed a red-shift in the CN stretch frequency with increasing dielectric constant of the surrounding liquid.
• The adapted Onsager model successfully explained the observed frequency shifts and estimated the interfacial reaction field.
• Highlighted the significant role of the metal surface in the solvation environment of interfacial molecules.

Conclusions:

• The developed interfacial reaction field model accurately describes electric fields at conductor-dielectric interfaces.
• This work provides fundamental insights into elusive interfacial electric fields and their impact on molecular properties.