Gas phase chain reaction of H2O2+ NO2+ CO

Abstract

Reactions in gas phase mixtures of H₂O₂ vapour, NO₂ and CO at 292±2 K have been studied by measurement of the variation of yield of the CO₂ product. It has been shown that the mechanism is the chain reaction sequence H₂O₂+ NO₂→ OH + HNO₃(1), OH + CO → CO₂+ H (2), H + NO → OH + NO (3), OH + NO₂(+M)→ HNO₃(+M)(4) provided that excess NO₂ is present. An estimate of k₄/k₂ is obtained which is rationalised in terms of reaction (4) being between second and third order for M = CO at pressures of 8 and 13.3 kN m^–2. Addition of n-butane to the mixture induces the reaction OH + n-C₄H₁₀→ H₂O + n-C₄H₉. (8). From the resultant decrease in the kinetic chain length a ratio of k₈/k₂= 14.8 ± 0.9 is deduced, in good agreement with ratios of available absolute values of k₈ and k₂. It is considered that the H₂O₂+ NO₂+ CO + substrate reaction system provides a useful non-photolytic source of OH + substrate rate constant data relative to k₂, of wider application than photolytic sources so far developed.