Rapid crystallization of amorphous solid water by porosity induction

Area of Science:

• Astrochemistry
• Materials Science
• Physical Chemistry

Background:

• Amorphous solid water (ASW) typically crystallizes at higher temperatures (155 K) through bulk nucleation.
• Understanding ASW crystallization is crucial for astrophysical environments where ice plays a significant role.

Purpose of the Study:

• To investigate a novel method for rapid ASW crystallization using acetonitrile (ACN).
• To explore the mechanism of ACN-induced ASW crystallization and its kinetics.
• To assess the relevance of this process to astrophysical ice formation.

Main Methods:

• Preparation of sandwich films: acetonitrile (ACN) and ASW (ACN@ASW, ASW@ACN) in ultrahigh vacuum (UHV).
• Utilized an HDO probe layer within ASW to track crystallization.
• Analyzed crystallization kinetics and activation energy (Ea) using the Avrami equation.

Main Results:

• Demonstrated rapid ASW crystallization at 128-134 K, well below the normal 155 K, induced by ACN diffusion-desorption.
• Observed simultaneous crystal growth from both top and bottom surfaces into the ASW bulk.
• Calculated an activation energy (Ea) of ~53 kJ mol⁻¹, consistent with crystal growth and suggesting minimal nucleation.

Conclusions:

• ACN diffusion-desorption is an effective mechanism for rapid ASW crystallization.
• The observed crystallization process, characterized by low activation energy and simultaneous growth, supports its occurrence in astrophysical settings.
• This finding offers a potential explanation for crystalline ice formation in various cosmic environments.