Valence Electronic Structure of Interfacial Phenol in Water Droplets

Area of Science:

• Physical Chemistry
• Surface Science
• Spectroscopy

Background:

• Chemical reactions in aqueous environments are crucial for biochemistry and atmospheric chemistry.
• Understanding molecular behavior at aqueous interfaces requires knowledge of valence electronic structure.
• Photoelectron spectroscopy is a sensitive probe for studying electronic states in aqueous systems.

Purpose of the Study:

• To investigate the valence electronic structure of aqueous phenol droplets using velocity-map photoelectron imaging.
• To examine the concentration-dependent effects on the vertical binding energy (VBE) of phenol in aqueous droplets.
• To compare nonresonant and resonance-enhanced two-photon ionization pathways.

Main Methods:

• Velocity-map photoelectron imaging of submicrometer-sized aqueous phenol droplets.
• Femtosecond ultraviolet light for nonresonant (288 nm) and resonance-enhanced (274 nm) two-photon ionization.
• Concentration-dependent studies from 0.01 M to 0.8 M phenol.

Main Results:

• Nonresonant ionization showed a decrease in VBE from 8.0 eV (0.01 M) to 7.6 eV (0.8 M) with increasing phenol concentration.
• This VBE shift is attributed to phenol dimer and aggregate formation at the droplet surface.
• Resonance-enhanced ionization exhibited a concentration-independent VBE of ~8.1 eV, due to ultrafast relaxation and excimer/aggregate formation.

Conclusions:

• Phenol aggregation at aqueous droplet surfaces significantly influences its electronic structure and photoionization behavior.
• Resonance-enhanced ionization provides insights into ultrafast dynamics, bypassing concentration-dependent surface effects.
• Electron transport scattering within droplets can affect measured VBEs, requiring corrections.