Ethynyl Radical Hydrogen Abstraction Energetics and Kinetics Utilizing High-Level Theory

Area of Science:

• Physical Chemistry
• Astrochemistry
• Combustion Chemistry

Background:

• The ethynyl radical (C2H) is prevalent in interstellar space, planetary atmospheres, and combustion of alkynes.
• Hydrogen-atom abstraction is a key reaction pathway for the ethynyl radical in diverse environments.

Purpose of the Study:

• To investigate the C2H + HX reactions, where HX includes HNCO, HONO isomers, C2H4, and CH3OH.
• To accurately determine reaction barriers and kinetics for these reactions using high-level theoretical methods.

Main Methods:

• Employed high-level theoretical calculations, including CCSD(T)-F12a/cc-pVTZ-F12, with extended basis sets (aug-cc-pV5Z) and methods up to CCSDT(Q).
• Included core correlation and additive energy corrections to achieve subchemical accuracy (≤0.5 kcal mol⁻¹) for stationary point enthalpies.
• Calculated reliable kinetics over a broad temperature range (50–5000 K).

Main Results:

• Predicted significantly lower energy barriers for C2H + HNCO (2.19 kcal mol⁻¹) and C2H + C2H4 (0.47 kcal mol⁻¹) compared to previous studies.
• Obtained accurate thermodynamic data and kinetic parameters for the investigated reactions.
• Ensured high precision in calculated relative enthalpies, converging to subchemical accuracy.

Conclusions:

• The refined theoretical calculations provide accurate insights into the reactivity of the ethynyl radical.
• The predicted low barriers suggest these reactions may be more significant in interstellar and combustion environments than previously assumed.
• The generated kinetic data can guide future experimental investigations and modeling efforts.