Electron spin echo signal

Studying the electron tracks with the Monte Carlo method, the authors of Refs. 302 and 303 have used the so-called stochastic approach, within which one fixes a simultaneous picture of the spatial distribution of excitation and ionization events. The tracks found this way are sets of spatial points where the inelastic scattering events took place. With this at hand it proves to be possible to calculate the energy absorption spectrum in sensitive volumes of the irradiated medium303 and to calculate the shape of the line and the slope of electronic spin echo signals.302 Such a... 

Long range dipolar interactions between an unpaired electron and nuclear spins on adjacent atoms will not normally be resolved in conventional powder EPR spectra.The pulse technique of electron spin echo modulation (ESEM) is in favourable cases able to detect very weak hyperfine interactions not seen in CW EPR. The method measures modulation of the electron spin echo signal by dipolar hyperfine coupling in the time domain at fixed magnetic field. Until recently,... 

An intensity change of the electron spin echo signal occurs when a RF pulse with a frequency corresponding to a nuclear spin transition is applied. An ENDOR spectrum is obtained by sweeping the RF frequency. Some well-established methods are named after their inventors. Mims-ENDOR [46] is a stimulated echo sequence with a RF pulse inserted between the second and third mw-pulses. The method is particularly used for measurements of small hyperfine couplings. Another pulse technique for performing ENDOR devised by Davies [47] is also commonly employed. The pulse sequence for this method is shown in Fig. 2.26. 

FIGURE 9 Illustration of a two-pulse electron spin-echo signal. Microwave pulses 1 and 2 separated by time x produce the echo signal V at a second time r after pulse 2. As r Is Increased the echo amplitude generally decreases, and in solids the amplitude may be modulated as shown here. The decrease in echo amplitude Is related to transverse magnetic relaxation times, and the modulation Is related to weak anisotropic hyperfine coupling to nearby magnetic nuclei. 

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

To determine whether PLP was actually associated with the lysine radical, [4 - H]PLP was synthesized and exchanged into the enzyme, and the [4 - H]PLP-enzyme was used to prepare a sample of the putative product radical 3. The EPR spectrum of the sample containing [4 - H]PLP proved to be identical with that of a matched sample containing PLP. The two samples were submitted to electron spin echo envelope modulation spectroscopy (ESEEM). The ESEEM spectra revealed a signal corresponding to the Larmor frequency for deuterium in the sample containing [4 - H]PLP (Fig. 5) and no signal in the PLP sample. This meant that the deuterium in [4 - H]PLP must be... 

In the last few years, pulsed EPR or electron spin echo (ESE) and reaction yield detected magnetic resonance (RYDMAR) techniques have been added to the arsenal of EPR techniques applied in photosynthesis. ESE combines high temporal resolution (currently 100 ns) with sensitivity to broad EPR signals, and it allows rapid and accurate determination of the spin-lattice and spin-spin relaxation times. 

A comparatively recent new development in ENDOR spectroscopy is electron spin echo ENDOR (ESE-ENDOR), where nuclear spin transitions are detected by their effect on a transient EPR signal (the spin echo) generated by a two- or three-pulse excitation. 

Spin echo spectroscopy is a definitive technique for determining the binding of imidazole to copper complexes. Detection of spin echo signals is based on the weak coupling of the electron to the unbound imidazole nitrogen, rather than the bound... 

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