How CO2 gas accelerates water nucleation at low temperature

Area of Science:

• Physical Chemistry
• Chemical Physics
• Thermodynamics

Background:

• Homogeneous nucleation is crucial for atmospheric and industrial processes.
• Understanding nucleation mechanisms at the molecular level is essential for process optimization.
• Binary nucleation studies provide insights into intermolecular interactions and cluster formation.

Purpose of the Study:

• To investigate homogeneous nucleation of binary H2O-CO2 mixtures.
• To determine the effect of CO2/H2O ratio on nucleation rates.
• To elucidate the role of transient hetero-molecular interactions in nucleation.

Main Methods:

• Experiments conducted using dilute binary H2O-CO2 mixtures in Ar-N2 carrier gas.
• Utilized Laval expansions for controlled nucleation conditions.
• Mass spectrometric detection of nucleating clusters to analyze composition and concentration.

Main Results:

• Observed only homo-molecular water clusters in mass spectra.
• Found a significant increase in nucleation rate with increasing CO2/H2O ratio.
• A kinetic model indicated transient H2O-CO2 dimers accelerate nucleation.

Conclusions:

• Hetero-molecular interactions, even transient ones, can significantly enhance nucleation rates.
• Nucleation efficiency is influenced by intermolecular forces and molecular degrees of freedom.
• Molecular-level studies are vital for understanding complex nucleation phenomena.