Proton distribution

Distribution of protons by type and overall aromatic/aliphatic proton ratios for the original fractions and bottoms products, as determined by proton nmr. Proton distribution for fraction D and the whole coal are not included as these materials were only partly soluble and the resultant spectra were not representative of the whole material. 

Anti-protonic atoms. Recently neutron density distributions in a series of nuclei were deduced from anti-protonic atoms [30], The basic method determines the ratio of neutron and proton distributions at large differences by means of a measurement of the annihilation products which indicates whether the antiproton was captured on a neutron or a proton. In the analysis two assumptions are made. First a best fit value for the ratio I / of the imaginary parts of the free space pp and pn scattering lengths equal to unity is adopted. Secondly in order to reduce the density ratio at the annihilation side to a a ratio of rms radii a two-parameter Fermi distribution is assumed. The model dependence introduced by these assumptions is difficult to judge. Since a large number of nuclei have been measured one may argue that the value of Rj is fixed empirically. 

EVB-based MD simulahons, as well as conhnuum dielectric approaches, involve empirical correlations between the structure of acid-functionalized interfaces in PEMs and proton distributions and mobilities in aqueous domains. The results remain inconclusive with respect to the role of packing... 

Pore size and dielectric constant s of water in pores exhibit a strong effect on proton distributions, as studied in Eikerling. Model variants that take into account the effect of strongly reduced s near pore walls ° and the phenomenon of dielectric saturation ° 2° lead to nonmonotonous profiles in proton concentration with a maximum in the vicinity of the pore wall. 

Figure 3. Activation energy for conversion to THF solubles vs. aliphatic hydrogen for Argonne Premium Coal sample bank bituminous coals. Data on proton distribution from Dr. Charles Bronnimann, Colorado State University.

Molecular dynamics simulations were used to compute proton distributions on faceted a-FeOOH particles 3-8 nm in size (40). 

Fig. 3. The transient absorption pertaining to peroxynitrite measured as a function of [Ft]. The reaction kinetics are compared to those predicted by diffusion models assuming a. steady-state and b. time-dependent proton distribution.

Another question we might pose to ourselves is whether the neutron and proton distributions in nuclei are the same Modern models for the nuclear potential predict the nuclear skin region to be neutron-rich. The neutron potential is predicted to extend out to larger radii than the proton potential. Extreme examples of this behavior are the halo nuclei. A halo nucleus is a very n-rich (or p-rich) nucleus (generally with low A) where the outermost nucleons are very weakly bound. The density distribution of these weakly bound outermost nucleons extends beyond the radius expected from the R °c A1 /3 rule. Examples of these nuclei are nBe, nLi, and 19C. The most well-studied case of halo nuclei is 1 Li. Here the two outermost nucleons are so weakly bound (a few hundred keV each) as to make the size of 11 Li equal to the size of a 208Pb nucleus (see Fig. 2.12). 

The parameters of Hamiltonians (1) and (2) are determined in our approach by pure theoretical way using different quantum chemical models and calculations unlike the traditional fitting the experimental thermodynamic and dielectric data. Our method of the many-pseudospin clusters [ 1,4] seems to be the most reliable way of determination. The latter are obtained in this case within the static approximation from the system of equations for a typical crystal fragment (cluster) for all possible proton distributions on H-bonds. The left-hand side of any equation expresses the cluster total energy in terms of Jy, while the right-hand side is determined by means of the quantum chemical calculation of this energy. 

The isobacteriochlorin 8 serves as an example. Two protons distributed between the four nitrogen atoms with a 50% occupancy at each site were found experimentally. It has been suggested that two tautomeric forms (8a, b) contribute, equally to the solid-state structure. Two Ca—N bonds (A = 0.051 A) and two C —Cm bonds (A = 0.077 A) are significantly different as a result of the superposition of the tautomeric forms (82JA2376). 

When using the thermal process for the production of SCT pitch, the temperature and time are important process parameters. The higher the temperature used, the higher is the aromaticity and condensation of the aromatic rings. The average carbon and proton distributions (determined by Nuclear Magnetic Resonance Spectroscopy) of SCT pitches prepared by thermal process at 390°C and 430°C are presented in Table III. 

Table III Effect of Thermal Process Temperature on the Carbon and Proton Distribution in SCT-Pitch...

Table II. Proton Distribution and Structural Parameters of Coal-Liquid Fractions (7)...

Bivalent cations also affect the proton distribution if small cages have been filled, e.g., with Mg ions, the protons that are created during the reduction of a transition metal ion will predominantly stay in the supercages, where they interact with the metal clusters, as will be described in more detail below. Because such adducts can act as very active sites, a catalyst promoter effect of Ca and Mg on reduced Pd has therefore been attributed, in part, to the enhanced concentration of metal-proton adducts in accessible supercages (765). 

Proton studies using MQ techniques have been made to determine the proton distribution in systems such as hydrogenated amorphous silica films (Levy and Gleason 1993a) and silicon carbide (Petrich et al. 1987). Hydrogen doping of carbon-based... 

Zeng et al. (1999) employed H- Al and H- Na TRAPDOR in combination with H mas to investigate the proton distribution in 4 hydrous aluminosilicate glasses. Peaks at 6 and 2.9 ppm correspond to 2 different water environments while others at 5-6, 3.5 and 1.5 ppm arise from 3 different hydroxyls. Rapid exchange occurs at room temperature between the 2 water environments. The data reveal the complexity of the proton speciation in these materials. All the resonances show a TRAPDOR effect to some extent. One of the groups identified is AlQ -OH, implying that the aluminosilicate framework is depolymerised by the water. This conclusion does not agree... 

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