Many-quantum transitions in conduction electron spin resonance

1968 ◽  
Vol 46 (15) ◽  
pp. 1685-1689
Author(s):  
T. A. Koss ◽  
S. Alexander ◽  
C. F. Schwerdtfeger
Keyword(s):  
Spin System ◽  
Bloch Equation ◽  
Effective Field ◽  
Resonance Absorption ◽  
Rotating Frame ◽  
Conduction Electrons ◽  
Spin Resonance ◽  
Quantum Transitions ◽  
Theory And Experiment ◽  
Modified Bloch Equation

Resonance absorption spectra have been observed which may be interpreted as many-quantum transitions where the quantization is along the effective field in the rotating frame. The spin system used was that of the conduction electrons in Li metal in a crystal of neutron irradiated LiF. An analysis of the experimental results using a modified Bloch equation under the assumptions that [Formula: see text] and that the spin system relaxes towards the instantaneous field is presented. The agreement between theory and experiment is excellent.

Microwave Spin Resonance Absorption by Conduction Electrons in Metallic Sodium

1952 ◽  
Vol 88 (4) ◽  
pp. 951-952 ◽  
Author(s):  
T. W. Griswold ◽  
A. F. Kip ◽  
C. Kittel
Keyword(s):  
Resonance Absorption ◽  
Metallic Sodium ◽  
Conduction Electrons ◽  
Spin Resonance

Article

1999 ◽  
Vol 77 (11) ◽  
pp. 1810-1812 ◽  
Author(s):  
Alex D Bain
Keyword(s):  
Spin System ◽  
Coupled System ◽  
Coupled Systems ◽  
Physical Reason ◽  
Strongly Coupled ◽  
System Combination ◽  
First Order ◽  
Weakly Coupled ◽  
Quantum Transitions ◽  
Weakly Coupled Systems

Strongly coupled spin systems provide many curious and interesting effects in NMR spectra, one of which is the presence of unexpected (from a first-order viewpoint) lines. A physical reason is given for the presence of these combination lines. The X part of the spectrum of an ABX spin system is analysed as an example. For an ABX system, it is well known that the AB nuclei give a spectrum consisting of two AB-type spectra, corresponding to the two orientations of the X nucleus. It can also be shown that the X part of the spectrum corresponds to the X nucleus undergoing a transition in the presence of an AB-like spin system. For weakly coupled systems, the four observed lines correspond to the four different orientations of the A and B nuclei. For a strongly coupled system, two additional lines may appear, the combination lines. The resulting six lines correspond to the four spin orientations, plus the two zero-quantum transitions. It is shown that these six lines are such that there is no net excitation of the AB-like spin system associated with the X transitions. There is no AB coherence created directly by a pulse applied to X. AB coherence is created as the system evolves, and this is responsible for many of the curious effects. This is shown to be true for all spin sub-systems, which are weakly coupled to a strongly coupled sub-system.Key words: NMR, strong coupling, second-order spectra, ABX spin system, combination lines, spectral analysis.

Light-induced reversible ionization of tetramethylphenylenediamine in an inorganic polymer of n-butyl orthotitanate

1988 ◽  
Vol 66 (8) ◽  
pp. 1931-1935
Author(s):  
Hisashi Ueda ◽  
Masahiro Kaise
Keyword(s):  
Relaxation Time ◽  
Electron Spin Resonance ◽  
Visible Light ◽  
Relative Intensity ◽  
Hyperfine Splitting ◽  
Resonance Absorption ◽  
Spin Quantum ◽  
Spin Quantum Number ◽  
Spin Resonance ◽  
Intensity Ratios

n-Butyl orthotitanate, BT, polymerized in tetrahydrofuran, if irradiated by visible light, gives a new electron spin resonance absorption that is not found before irradiation. In the present work, three different polymers of BT were synthesized by adding tetramethyl phenylenediamine (TMPD), dimethyl phenylenediamine (DMPD), or phenylenediamine (PD), to the solution of BT. The polymers thus prepared were tested to see if they give a new esr signal when irradiated by visible light. The polymer to which 1 mol% of TMPD was added gave TMPD•+ when irradiated by visible light, but the TMPD•+ signal decayed after the irradiation was discontinued. This change, therefore, is reversible. The resonant position of every hyperfine splitting line of the TMPD•+ found in this polymer coincided with that of TMPD•+ in solution, but the relative intensity ratios and the line width of each line depended on the nuclear spin quantum number of the coupling nuclei. This can be interpreted by the restricted rotational motion of TMPD•+ in the polymer matrix. The contribution of the non-diagonal term to the spin relaxation time would explain this phenomenon. In the case of the polymer to which DMPD was added, a small amount of DMPD•+ seemed to be formed, but no radical was detected in the case of the polymer to which PD was added.

Applications of ESR to Carbonaceous Materials

1982 ◽  
Vol 36 (1) ◽  
pp. 52-57 ◽  
Author(s):  
L. S. Singer ◽  
I. C. Lewis
Keyword(s):  
Free Radicals ◽  
Electron Spin Resonance ◽  
Low Temperature ◽  
Electron Spin ◽  
Paramagnetic Species ◽  
Carbonaceous Materials ◽  
Conduction Electrons ◽  
Spin Resonance ◽  
Higher Temperature ◽  
Low Temperature Pyrolysis

The applications of electron spin resonance (ESR) to carbonaceous materials are reviewed. The stable paramagnetic species observed in the products of low-temperature pyrolysis are odd-alternate neutral free radicals, whereas the unpaired spins of higher temperature carbons and graphites are primarily conduction electrons. The variety of ESR properties and phenomena requires special attention to techniques of measurement and interpretations of results. The relevance to the carbonization process of the free radicals observed by ESR is also discussed.

Mechanism of Hydrogen Embrittlement of Austenitic Steels

2007 ◽  
Vol 539-543 ◽  
pp. 4249-4254 ◽  
Author(s):  
V. Shivanyuk ◽  
Valentin G. Gavriljuk ◽  
Jacques Foct
Keyword(s):  
Hydrogen Embrittlement ◽  
Line Tension ◽  
Austenitic Steels ◽  
Hydrogen Atoms ◽  
Conduction Electrons ◽  
Metallic Character ◽  
Spin Resonance ◽  
Localization Of Plastic Deformation ◽  
Dislocation Sources ◽  
Strain Dependent

Three main hypotheses of hydrogen embrittlement (HE) of austenitic steels are discussed based on the studies of the interatomic interactions, hydrogen-induced phase transformations and dislocations properties. Measurements of electron spin resonance and ab initio calculations of the electron structure witness that the concentration of conduction electrons increases due to hydrogen, which enhances the metallic character of interatomic bonds. The hypothesis of brittle hydrogen-induced phases is disproved by the studies of the silicon-alloyed steels: the silicon-caused increase in the fraction of the εH martensite is accompanied by the decrease of HE. Studies of strain-dependent internal friction have shown the hydrogen-caused decrease in the start stress of microplasticity and increase in the velocity of dislocations in accordance with HELP hypothesis. A mechanism of HELP is proposed based on the hydrogencaused enhancement of the metallic character of interatomic bonds, which results in the local decrease of the shear modulus within the hydrogen atmospheres round the dislocations. As consequence, the line tension of the dislocations followed by the hydrogen atoms decreases, which finds its expression in the early start of dislocation sources, decreased distance between dislocations in the pile-ups and increased velocity of dislocations. A mechanism of localization of plastic deformation is proposed based on the observations of the hydrogen-enhanced concentration of equilibrium vacancies.

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