Elucidating how trace gases interact with ice surfaces utilizing sum frequency generation spectroscopy.

Area of Science:

• Atmospheric Chemistry
• Surface Science
• Spectroscopy

Background:

• Trace gas interactions with ice surfaces are critical for atmospheric chemistry, influencing ozone depletion and aerosol formation.
• Understanding molecular adsorption on ice is key to comprehending the impact of hosted molecules and subsequent chemical reactions.

Purpose of the Study:

• To gain a molecular-level understanding of ice-trace gas interactions using surface-selective techniques.
• To probe ice surfaces and observe the adsorption of small organic molecules like acetone and methanol.

Main Methods:

• Utilizing sum frequency generation (SFG) spectroscopy, a surface-selective technique.
• Analyzing the structure of water molecules at ice and water interfaces with and without adsorbed molecules.

Main Results:

• Observed significant differences in water molecule structure at ice/water interfaces upon addition of acetone and methanol.
• Methanol-ice interface showed a blue shift (~80 cm⁻¹) indicating weakened hydrogen bonds, contrasting with acetone-ice interface's red shift (~10 cm⁻¹).

Conclusions:

• The distinct behaviors of water molecules and organic compounds at interfaces are linked to varying reactivity and photochemical reaction rates.
• Observed frequency shifts at interfaces can impact atmospheric models, particularly concerning overtone pumping reactions.