Growth of Clathrate Hydrates in Nanoscale Ice Films Observed Using Electron Diffraction and Infrared Spectroscopy

Area of Science:

• Materials Science
• Astrochemistry
• Physical Chemistry

Background:

• Clathrate hydrates (CHs) are prevalent in cold space environments like comets and icy moons.
• Previous research primarily used spectroscopy for CH formation studies, lacking direct structural data.
• Electron diffraction offers a potential method for characterizing CH structures in laboratory settings.

Purpose of the Study:

• To perform the first electron diffraction study on tetrahydrofuran (THF) and 1,3-dioxolane (DIOX) clathrate hydrates.
• To structurally characterize nanometer-thin ice films of THF and DIOX CHs under ultrahigh vacuum and cryogenic conditions.
• To compare electron diffraction data with X-ray diffraction and infrared spectroscopy for comprehensive analysis.

Main Methods:

• Formation and characterization of THF and DIOX clathrate hydrates as nanometer-thin ice films.
• Utilized reflection high-energy electron diffraction (RHEED) for structural analysis.
• Employed reflection absorption infrared spectroscopy (RAIS) for complementary data.

Main Results:

• THF CH readily formed on various substrates during thermal annealing of amorphous THF/water ice.
• DIOX CH formation on a Au(111) substrate showed similar growth patterns.
• Electron diffraction patterns confirmed the formation of structure II CH (5¹²6⁴) for both THF and DIOX, with a lattice constant of ~17.2 Å.

Conclusions:

• Electron diffraction successfully characterized THF and DIOX clathrate hydrates, confirming structure II formation.
• The findings provide crucial direct structural insights into CHs relevant to astrochemistry.
• Combining diffraction and spectroscopic techniques enhances the understanding of complex molecular interactions in CHs.