Methanol Formation in Hyperthermal Oxygen Collisions with Methane Clathrate Ice

Area of Science:

• Astrochemistry
• Planetary Science
• Chemical Kinetics

Background:

• Small organic molecules on airless icy bodies are crucial for prebiotic chemistry.
• The origin of these molecules remains an area of active research.

Purpose of the Study:

• To investigate the role of hyperthermal reactive ions in modifying the organic composition of ice.
• To simulate the bombardment of carbon-bearing ice by hyperthermal water group molecules.

Main Methods:

• Employed molecular dynamics simulations using the ReaxFF formalism.
• Simulated bombardment of methane (CH4) clathrate ice with hyperthermal water group molecules (H2O, x = 0-2) at energies of 2-58 eV.

Main Results:

• Methanol is the dominant organic product from atomic oxygen irradiation of CH4 clathrate at low doses, with yields up to 10%.
• A novel hot-atom reaction mechanism is the primary pathway for methanol formation, with radiolysis playing a secondary role.
• At high irradiation doses, carbon oxidation states increase, favoring formaldehyde over methanol.
• Other water group impactors are less effective, and CO/CO2 clathrates are resistant to hydrogenation.

Conclusions:

• Hyperthermal reactive ions significantly influence the organic inventory of icy bodies.
• The formation of methanol via hot-atom mechanisms is a key process in extraterrestrial organic synthesis.
• Irradiation dose and impactor type dictate the resulting organic composition and oxidation states.