Proton magnetic moment distribution

From precise data on the differential scattering as a function of angle at even higher energies, it is hoped to obtain information on the shape of the proton charge and magnetic moment distribution. Preliminary results of such measurements have been reported verbally. ... 

The so-called static dephasing regime (SDR) predicts a linear dependence of I/T2 on the magnetic moment of the particles in solution (22, 25). This regime describes the transverse relaxation of homogeneously distributed static protons in the presence of static, randomly distributed point dipoles. The free induction decay rate, I/T2, is then proportional to the part of the sample magnetization due to the dipoles (p), M = rap, where ra is the concentration... 

Both Ti and T2 relaxations of water protons are mainly due to fluctuating dipole-dipole interactions between intra- and inter-molecular protons [62]. The fluctuating magnetic noise from all the magnetic moments in the sample (these moments are collectively tamed the lattice) includes a specific range of frequency components which depends on the rate of molecular motion. The molecular motion is usually represented by the correlation time, xc, i.e., the average lifetime staying in a certain state. A reciprocal of the correlation time corresponds to the relative frequency (or rate) of the molecular motion. The distribution of the motional frequencies is known as the spectral density function. 

A further structure effect, the proton polarizability, is only estimated to be < 4 ppm [28], of the same order than the value above. The agreement between theory and experiment is therefore only valid on a level of 4 ppm. Thus, we can say that the uncertainty in the hyperfine structure reflects dominantly the electric and magnetic distribution of the proton, which is related to the origin of the proton anomalous moment, being a current topics of particle-nuclear physics. 

Although at pH 8 the electron distribution favours the formation of flavin semiquinone and reduced iron-sulfur center, the magnetic moments of the two redox centers do not interact. At pH 10, however, 2-electron-reduced TMADH exhibits the EPR spectrum diagnostic of the spin-mteracting state. In a more detailed analysis using the pH-jump technique, the interconversion of three states of TMADH [state 1, dihy-droflavin-oxidised 4Fe-4S center (formed at pH 6) state 2, flavin semi-quinone-reduced 4Fe-4S center (formed at pH 8) state 3, spin interacting state (formed at pH 10)] were studied in both H2O and D2O (Rohlfs et al., 1995). The kinetics were found to be consistent with a reaction mechanism that involves sequential protonation/deprotonation and electron transfer events (Figure 6). Normal solvent kinetic isotope effects were observed and proton inventory analysis revealed that at least one proton is involved in the reaction between pH 6 and 8 and at least two protons are involved between pH 8 and 10. At least three protonation/... 

The variation of the data from the point charge theory can be accounted for on the assumption that both the charge and magnetic moment of the proton are spread out over a finite distance. On the assumption that the magnetic moment and electric charge have the same distribution, they find that a root mean square ra us of about 7X10" cm fits the data they have obtained at several energies up to 236 Mev. 

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