Stoichiometry and rate of reaction of hydrogen atoms with oxygen

Abstract

The reaction of hydrogen atoms (10^–6–10^–5 mol dm^–3) with oxygen (0–10^–5 mol dm^–3) in excess argon has been studied in a fast flow—discharge tube at total pressures from 2 to 10 Torr and temperatures from 231 to 512 K using mass spectrometry and gas chromatography for final-product analysis. A method of measuring small concentrations of water (ca. 10^–7 mol dm^–3) has been developed which enabled the relative rates of reactions (2) and (3) to be determined, reaction (4) being negligible: H + O₂+ Ar → HO₂+ Ar (1), H + HO₂→ H₂+ O₂(2), H + HO₂→ 2OH (3), H + HO₂→ H₂O + O. (4). Over the range 231 < T/K < 464, log₁₀(k₃/k₂)=(1.44 ± 0.39)–(320 ± 120/T)(errors throughout are standard deviations).

An improved Arrhenius expression for reaction (1) has been determined k₁/dm⁶ mol^–2 s^–1=(2.85 ± 1.27) x 10⁸ exp [(796 ± 159)/T]. Previous evaluations of rate data for step (3) are discussed and revised values suggested log₁₀(k₃/dm³ mol^–1 s^–1)=(10.45 ± 0.36)–(120 ± 120)/T, log₁₀(k₂/dm³ mol^–1 s^–1)=(9.01 ± 0.53)+(200 ± 170)/T.