H-atom reactions

Gutierrez MS, Henglein A, Dohrmann JK (1987) H atom reactions in the sonolysis of aqueous solutions. J Phys Chem 91 6687-6690... 

It is unnecessary to require two neighbouring activated sites for the dissociative adsorption of N2. The effect of the promotor is not a strictly localized one but influences also the neighbourhood. At the typical concentrations of K+ it is rather unlikely that two neighbour sites are both activated. Thus our rales take into account the fact that an activated site also influences the energetic behaviour of the neighbouring sites. The dissociative adsorption of H2 can take place on every pair of free sites Si-Si, S1-S2 or S2-S2. The concentration of S] is a measure for the concentration of K+ on the surface. If N atom is the nearest neighbour of a H atom reaction occurs to HN — Si,2. Via further reaction steps the product molecule NH3 is formed which desorbs immediately after formation. We neglect recombination reactions. Therefore the basic reaction steps are... 

Wojnarovits L, Takacs E, Dajka K, Emmi SS, Russo M, D Angelantonio M (2004) Re-evaluation of the rate constant for the H atom reaction with fm-butanol in aqueous solution. Radiat Phys Chem... 

It is, however, quite plausible to assume that under these conditions the recombinations of H atoms (reaction 23), H + C2H5 (reaction 12), and probably CH3 + H (reaction 22) arc negligible compared to the other processes, since the latter undoubtedly require three-body collisions for stabilization. In this case, II is unimportant in chain-ending steps and Fa. (XIII.11.4) reduces to... 

A convenient way to study the kinetics and the mechanisms of H atom reactions in solution is to generate them by the pulse radiolysis of aqueous solutions at a low pH. Acetamide radicals, CH2C(=0)NH2, were identified in the pulse radiolysis of aqueous solutions of a-(methylthioacetamide), H3C-S-CH2C(=0)NH2, by time-resolved electron spin resonance (TRESR) spectroscopy. Only three mechanisms seemed plausible for such an observation. The first possibility is a two-step mechanism with an H-abstraction [reaction (27)] ... 

These subsequent reactions of OH and O are all sufficiently fast that [O] and [OH] never become comparable with [H]. Reactions (xxi) and (xxii) of OH and O with HO do not therefore become important in these room temperature systems where the initial radical is the H atom. Reactions (viii) and (xx) are also sufficiently fast that [HOj ] never becomes large enough for reaction (x) to need consideration. 

Similar conclusions were drawn for H-atom reactions [17] and the resulting general expression for the reaction with large (more than 4 carbon atoms) was obtained... 

The structures of chemical species have to be stored in a form which can be manipulated easily by the reaction generator that will predict the products of each elementary reaction. The computer representation must be unique and non-ambiguous so that reaction steps are not misinterpreted or repeated. As an example, for the neopentane + H atom reaction ... 

H atoms reactions with solutes can be carried out alone below pH 2 in or Ar saturated solutions containing 0.2 - 1 mol I" tert-butanol. 

Reductions by e are performed in N2 or Ar saturated solutions above pH Sand in the presence of 0.2 - 1 mol r tert-butanol (there is a small contribution from the H atom reactions). Radicals formed from tert-butanol are also present. 

In addition to thc above polymerization and recombination reactions, fragmentation of large carbon clusters (m > 30) due to collisions with H atoms and recombination of C2 H clusters with H atoms, reactions 7.6 and 7.7, may also be responsible for the production of C2 H2 (n = 4-8) polyynes. 

Here Ef is the amplitude, t the duration, and co the frequency of the ith pulse. This scheme has been applied in Ref [46] to a generic two-dimensional HT model which incorporated a H-atom reaction coordinate as well as a low-frequency H-bond mode. In a subsequent work [47] the approach has been specified to a simple model of HT in thioacetylacetone. The Hamiltonian was tailored to the form of Eq. (4.1) based on the information available for the stationary points, that is, the energetics as well as the normal modes of vibration. From these data an effective two-dimensional potential was constructed including the H-atom coordinate as well as a coupled harmonic oscillator, which describes the 0-S H-bond motion. Although perhaps oversimplified, this model allowed the study of some principle aspects of laser-driven H-bond motion in an asymmetric low-barrier system. 

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