Proton affinity of water and the mechanism and kinetics of production of H3O+ in flames of H2, O2 and N2
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 71, 1352-1362
- https://doi.org/10.1039/f19757101352
Abstract
From mass spectrometric measurements of the concentrations of H3O+ in flames of H2, O2 and N2 without additives, it is concluded that equilibrium levels of H3O+ are gradually attained in the burnt gases. These are governed by a balance of H + H + OH ⇌ H3O++e–(III) which in turn is affected by the species H and OH having concentrations above those for equilibrium especially in cooler flames. Observations made where process (III) is balanced demonstrate that its equilibrium constant is given by K3= 2.0 × 10–29 exp(–1.41 × 104K/T) cm3 molecule–1. This expression corresponds to a value for the proton affinity of water of 699 ± 17 kJ mol–1. H3O+ is thus produced in the burnt gases of these flames and the reaction responsible appears to be the forward step of (III), operating with an overall rate coefficient of 8.2 × 10–36 exp(–1.41 × 104K/T) molecule–2 cm6 s–1. The process is, however, thought to be a two stage one, rather than a true termolecular reaction. Application of the principle of microscopic reversibility indicates that the products from dissociative recombination of H3O+ and a free electron are two hydrogen atoms and a hydroxyl radical.Keywords
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