共查询到20条相似文献,搜索用时 0 毫秒
1.
J. M. Stadlbauer B. W. Ng Y. C. Jean Y. Ito D. C. Walker 《Hyperfine Interactions》1984,18(1-4):715-719
Using Muonium Spin Rotation (MSR) techniques the aqueous solution kinetics of several muonium addition reactions and spin conversion interactions have been studied. The addition reactions show both diffusion and activation-controlled reaction rates with isotope effects between 1 and 3 for diffusion-control and between 7 and 31 for activation-control reactions. Barrier energies are typically 15 kJ/mole and 30 kJ/mole, respectively, for these processes in water. Spin-conversion interactions involving Ni(aq
+2 and Ni(cyclam)+2 complexes showed that spin-conversion of triplet Mu by a paramagnetic solute occurs at or near the diffusion-controlled limit while the chemical reaction with the diamagnetic configuration of Ni(cyclam)+2 occured some 100 times slower at kM 5×108M–1s–1. 相似文献
2.
Masayoshi Senba 《Hyperfine Interactions》1991,65(1-4):779-791
The spin dynamics of the positive muon undergoing cyclic charge exchange (μ+⇌Mu) while it is slowing down is compared with that in the case of repeated muonium spin exchange after thermalization. The
expectation value of the spin polarization at timet aftern spin exchange collisions (att
1,t
2, ...,t
n
) are calculated explicitly from time dependent wave functions, and the quantity is averaged over the statistical distribution
of the times of collisions and over all possible numbers of collisions betweent=0 and the observation timet. This result is complementary and equivalent to the conventional density matrix formalism, but offers an insight into the
roles of spin flip and spin non-flip processes. The neutral fraction during slowing down is also discussed. 相似文献
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This paper brings together some current concepts concerning hydrogen states in semiconductors (illustrated with reference
to silicon but quite generally applicable) and highlight certain findings of recent quantum electronic structure calculations
for defect centres involving hydrogen and its isotopes. As regards muonium, the situation which held in the early μSR literature
[1] is entirely reversed: the location and structure of Mu* are now well established [2], whereas the precise location and the nature of the metastability of Mu′ have become open questions!
In fact, neither state is stable in the presence of other electrically active impurities, which undoubtedly accounts for the
difficulty in detecting paramagnetic protium. The implications for the interpretation of existing data, and for various possible
future experiments, are examined. 相似文献
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Rate constants for the reaction of muonium with benzene in water, methanol and n-hexane and for the reaction of muonium with
p-difluorobenzene, anilin, hexafluorobenzene and styrene are reported. All rate constants are below the calculated diffusion
controlled limit. The activation energy for the reaction of muonium with benzene in n-hexane is very small, indicating the
possibility of tunnelling by muonium. 相似文献
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C. Buci P. R. Crippa G. M. de'Munari G. Guidi M. Manfredi R. Tedeschi A. Vecli P. Podini 《Hyperfine Interactions》1979,6(1-4):425-429
Muonium's reaction constants with DNA and its constituents in water solutions are reported and compared with the available data for hydrogen. The low frequency spectrum of the resulting muonic radicals in low magnetic fields is recognized.This work was supported by Consiglio Nazionale delle Ricerche, contract no 75.00862.02 and by CERN, Experimental Physycs Division. Data analysis performed at CINECA computation facilities. 相似文献
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11.
James L. Cox 《Physics letters. A》1984,104(3):149-152
A portion of the charge induced in an isotropic plasma by an injected charged particle is shown to combine with the particle to form a charged quasi-particle, the effective charge, that is different from the conventional “dressed” charge. The remainder of the induced charge is found in a wake behind the effective charge. Properties of effective charge are described, and the application of this concept to coherent ion acceleration and stopping power is discussed. 相似文献
12.
R. Yu. Babkin K. V. Lamonova S. M. Orel Yu. G. Pashkevich V. F. Meshcheryakov 《Optics and Spectroscopy》2012,112(3):438-442
We propose a scheme for determining the effective nuclear charge Z efCF of a 3d ion placed in a crystal field of arbitrary symmetry. As an example, we consider the Co2+ ion in a matrix MCO3 (M = Ca, Cd). We show that the effective nuclear charge Z efCF correlates with a change in the degree of the bond covalence. 相似文献
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14.
Ali Asghar Mohammadi Salman Taheri Arman Amini Reza Ahdenov 《Molecular diversity》2018,22(4):999-1006
Triamide derivatives have been synthesized in good yields in a novel, one-pot, five-component, and efficient process by the reaction of Z-oxazolone, water, primary amines, aldehydes, isocyanides, in the presence of catalytic amount of KAl(SO4)2·12H2O (alum) as a non-toxic, reusable, inexpensive, and easily available reagent via Ugi reaction in aqueous solution. 相似文献
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The refined set of values of the effective nuclear charge (\(\bar Z_{ef} \)) and the set of one-electron spin-orbital constants (ξ 3d teor ) are obtained for ions of transition metals with the help of a semiempirical method of calculation of the spectrum of free ions with allowance for the spin-orbital interaction. The effective nuclear charge, which is a variable theoretical parameter, was determined from a comparison of theoretically calculated ion absorption spectra with experimental ones. The form of the potential for the calculation of the spin-orbital constant was chosen such that the calculated value ξ 3d teor would coincide with the experimental one ξ 3d exp . The calculated set of values \(\bar Z_{ef} \), ξ 3d teor } can be used in semiempirical calculations of energy levels of 3d ions (ions with an incomplete 3d shell). 相似文献
17.
Yuki Yamamoto Jun‐ya Hasegawa Yoshikatsu Ito 《Journal of Physical Organic Chemistry》2012,25(3):239-247
The kinetics of carbamate formation from the reaction of carbon dioxide with α‐amino acids in D2O was first investigated by means of nuclear magnetic resonance spectroscopy. Potassium carbonate was used as the CO2 source. For each amino acid, the maximum carbamate yield, the apparent rate constant for the carbamate formation kapp, and the rate constants for the formation k1 and the breakdown k?1 of the carbamate were estimated. Plots of log k1 or log k?1 versus pKa of amino acids indicated that the formation rate k1 increased with the basicity (pKa) of amino acid, while the decomposition rate k?1 decreased. A Br?nsted β value of 0.39 was obtained from the former plot, being in good agreement with the previously reported ones (0.26–0.43). The observed negative pKa dependence of log k?1 (Br?nsted α = 0.34) is reasonable, because the carbamate decomposition is acid‐catalyzed and the steady‐state concentration of H+ should be higher for weaker basic amines. The charge (σ) and the lone‐pair energy (EN) at the nitrogen atom of the amino group were calculated. Although log k1 correlated with σ and EN, log k?1 was unrelated with both of these parameters. Considering that the carbamate formation (k1) is not only base‐catalyzed but should also be promoted by the nucleophilicity of the amino nitrogen, its correlation with σ and EN in addition to pKa is rational. The irrelevance of log k?1 to σ and EN is not surprising, because σ and EN are not a direct measure of [H+] of the solution. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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E. S. Gusarevich 《Journal of Experimental and Theoretical Physics》2017,124(2):196-201
The energy losses of fast structural ions in collisions with atoms have been considered in the eikonal approximation. The structural ions are ions consisting of a nucleus and a certain number of electrons bound to it. The effect of nuclear charge Z of the ion on its effective deceleration κ(p) (energy losses associated with excitation of only intrinsic ion shells) has been analyzed. It is shown that the allowance for the interaction of an atom with the ion nucleus for Z a Z/v > 1, where Z a is the charge of the atomic nucleus and v is the velocity of collisions in atomic units, considerably affects the value of κ(p), which generally necessitates taking into account nonperturbatively the effect of both charges Z a and Z on κ(p). 相似文献
20.
Muonium-radicals resulting from insertion into the benzene ring are found to be much more prevalent in allyl benzene (C6H5CH2CH=CH2) than in styrene (C6H5CH=CH2). The salient implication of this comparison is that intramolecular rearrangements preceeded the μSR observation for the
case of styrene. In turn, this suggests that muonium-containing free radicals, as seen directly by kilogauss transverse field
μSR, are not necessarily theprimary radicals. Therefore, the elucidation of mechanism (and identification of the precursor) of Mu-radical formation is further
complicated by the fact that the observations may refer to thermodynamically more stable secondary radicals-those resulting
from a variety of intra-or inter-molecular relaxations or exchanges. Primary kinetic selectivities of thermalized muonium
atom addition reactions can be determined, however, through the substituent effect on the Hammett linear free energy parameter
in dilute solution. Results have been obtained for substituted benzenes and benzoic acids. Muonium apparently has a mild nucleophilic
character. And, most interestingly, this is opposite to that of its heavy isotope hydrogen. 相似文献