Mechanism, thermochemistry, and kinetics of the reversible reactions: C 2 H 3  + H 2 ⇌ C 2 H 4 + H ⇌ C 2 H 5 .

High-level coupled cluster theory, in conjunction with Active Thermochemical Tables (ATcT) and E , J -resolved master equation calculations, was used in a study of the title reactions, which play an important role in the combustion of hydrocarbons. In the set of radical/radical reactions leading to soot formation in flames, the addition of H-atoms to alkenes is likely a common reaction, triggering the isomerization of complex hydrocarbons to aromatics. The heats of formation of C ₂ H ₃ , C ₂ H ₄ , and C ₂ H ₅ are established to be 301.26 ± 0.30 at 0 K (297.22 ± 0.30 at 298 K), 60.89 ± 0.11 (52.38 ± 0.11), and 131.38 ± 0.22 (120.63 ± 0.22) kJ mol ^-1 , respectively. The calculated rate constants from first principles agree well with experiments where they are available. Under conditions typical of high temperature combustion - where experimental work is very challenging with a consequent dearth of accurate data - we provide high-level theoretical results for kinetic modeling.