Pulse Radiolysis of Methane

Area of Science:

• Physical Chemistry
• Radiation Chemistry
• Chemical Kinetics

Background:

• Understanding methane radiolysis is crucial for various chemical processes.
• Intermediates such as H, C, CH, CH2, CH3, and ions play significant roles.
• Electron and positive ion scavengers are used to probe reaction mechanisms.

Purpose of the Study:

• To define the role of key intermediates in methane radiolysis product formation.
• To investigate the mechanisms of ion neutralization and reactions with scavengers.
• To elucidate the kinetics and pathways governing methane radiolysis.

Main Methods:

• Pulse radiolysis of methane was conducted in the absence and presence of scavengers (SF6, CD3I, i-C4D10).
• Dose rate, dose, and pulse duration were systematically varied (0.68–15.2 × 10^19 eV/g-s, 3–100 ns).
• Product yields (ethylene, ethane) were analyzed to infer reaction mechanisms.

Main Results:

• H-atom reactions with accumulated ethylene explain yield variations with dose.
• Fast-reacting species (C, CH, 1CH2) insert into methane, forming products.
• Slowly reacting species (3CH2, CH3) contribute to product formation, evidenced by 3CH2 + CH3 → C2H4 + H.
• Ions undergo neutralization via specific processes, and reactions with i-C4D10 were quantified.

Conclusions:

• The study clarifies the complex reaction network in methane radiolysis.
• Specific roles of transient species and ions in product formation were identified.
• The neutralization rate constants for methane ions were determined and validated.