Recombination of hydrogen ion (H+) and hydroxide in pure liquid water

Natzle, W.; Moore, C. Bradley

doi:10.1021/j100258a035

Cited by 77 publications

(66 citation statements)

References 9 publications

(11 reference statements)

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“…The extraction of p(co), equation (15), for water and ionic solutions from IN6 inelastic spectra has already been performed [35,36] but it requires longer counting times than those used in the present experiment. So, we have restricted our analysis to a more qualitative level and chosen to present sums of ~o2S(Q, co)/QZ spectra for a better identification of the inelastic features.…”

Section: Inelastic Scatteringmentioning

confidence: 99%

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Neutron scattering study of the proton dynamics in aqueous solutions of sulphuric acid and caesium sulphate

Lassègues¹,

Cavagnat²

1989

Molecular Physics

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The quasielastic neutron scattering spectra of aqueous solutions of sutphuric acid have been recorded and compared to those of pure water and of caesium sulphate solutions in order to study the proton dynamics in these systems and in particular the abnormal proton diffusivity expected to occur in acidic solution. Mean transport coefficients for the water molecules' translational and rotational diffusive motions have first been determined in the three systems. They indicate a marked slowing down of the translational diffusion when salt or acid are added to water. The rotational motion is much less affected. In H2SO 4 solutions corresponding to the maximum of specific conductivity, some evidence is obtained for a weak and broad quasielastic component, not present in pure water or in Cs2SO~ solutions. Its analysis is reasonably accurate only for momentum transfer values Q lower than 0.5 A-1. In this low Q limit, the rotational contributions can be neglected and the spectra of the acidic solutions can simply be reproduced by the weighted sum of two lorentzian translational profiles. The more intense and narrower one corresponds to normal diffusion of solvation water molecules. We assign the broader additional component to the abnormal proton diffusivity. It contains about 12 per cent of the total intensity in agreement with the percentage of protons involved in n30 + species. The width of both components increases linearly with Q2 below Q = 0"5 A-1. In a H2SO 4 3.2 M solution at 263 K, mean water diffusion can be characterized by a diffusion constant D t = (0"53 "4-0"03) 10-9m2s 1 whereas the fast proton diffusion process is characterized by D § = (2.2 _ 0-4)10-8 m 2 s-1. The corresponding activation energies are respectively AE t = (18-4 + 0.4)kJ mol-1 and AE § = (8.4 _ 2)kJ mol-1. Thus, for the first time, a signature of the abnormal proton mobility is observed by neutron scattering.

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Section: Inelastic Scatteringmentioning

confidence: 99%

“…This is contested by others who prefer to call HsO ~ a transition state [14]. More recent studies conclude that a cluster of four molecules (H 9 O +) is the critical size for caging a proton [15,16]. This four molecules ion pair intermediate was actually proposed by Eigen in connection with a 6 to 8 A recombination distance [1].…”

Section: Introductionmentioning

confidence: 99%

Neutron scattering study of the proton dynamics in aqueous solutions of sulphuric acid and caesium sulphate

Lassègues¹,

Cavagnat²

1989

Molecular Physics

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“…The diffusion-limited ion association rate can be relevant for weak electrolytes, where the intrinsic association rate constants are large, and the dissociation rate constants are small. For example, the association rate of water can be estimated as k a = 1.3 × 10 11 L/(mol s) using the diffusion limited bulk rate constant 4π(D + + D − )R eff together with the effective reaction radius given by R eff = |r c |/[1 − exp(−|r c |/R)], [42][43][44][45] where |r c | = e 2 /(ǫk B T ) is the Onsager radius and the diffusion constants of H 3 O + and OH − are 9.4 × 10 −9 m 2 /s and 5.3 × 10 −9 m 2 /s, respectively. [46] In the above estimation, we also used ǫ = 80 and R = 0.75 nm.…”

Section: Interpretation Of the Linearization Conditionmentioning

confidence: 99%

Possible influence of the Kuramoto length in a photo-catalytic water splitting reaction revealed by Poisson–Nernst–Planck equations involving ionization in a weak electrolyte

Suzuki

Seki

2018

Chemical Physics

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We studied ion concentration profiles and the charge density gradient caused by electrode reactions in weak electrolytes by using the Poisson-Nernst-Planck equations without assuming charge neutrality. In weak electrolytes, only a small fraction of molecules is ionized in bulk. Ion concentration profiles depend on not only ion transport but also the ionization of molecules. We considered the ionization of molecules and ion association in weak electrolytes and obtained analytical expressions for ion densities, electrostatic potential profiles, and ion currents. We found the case that the total ion density gradient was given by the Kuramoto length which characterized the distance over which an ion diffuses before association. The charge density gradient is characterized by the Debye length for 1:1 weak electrolytes. We discuss the role of these length scales for efficient water splitting reactions using photo-electrocatalytic electrodes.

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“…Most of the acid-base neutralization studies have been interpreted within the framework of the model proposed by Eigen and de Maeyer in the 1960s [89]. This model attributes the rate-limiting step of recombination to the approach of the solvated species by a Grotthuss-like structural diffusion mechanism until a contact distance of about 6 Å where the contact ion pair is formed ( figure 9) [113]. The subsequent recombination is then a downhill process.…”

Section: (I) the Excess Protonmentioning

confidence: 99%