Spectrometer electron paramagnetic resonance

Czoch, R. and Francik, A. 1989. Instrumental Effects in Homodyne Electron Paramagnetic Resonance Spectrometers. Chichester Ellis Horwood. 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

If the two radicals were identical, the precession frequency of the two electrons would be precisely the same, and a particular radical pair would remain in whichever of the four states it found itself initially. But if the two radicals are different, the two electrons will have slightly different precession frequencies. The precession frequency of an electron is characterized by a quantity called the g factor. If one were to observe just one of the radicals of the pair in an electron paramagnetic resonance spectrometer, the value of its g factor would determine the position of the resonance line in the spectrum g of an electron in a radical is thus analogous to chemical shift of a proton. 

Electron Paramagnetic Resonance (EPR) Spectrometer [43-4 6]. When a paramagnetic or ferromagnetic sample (solid or liquid) of molecules or ions with total spin S and magnetization M is placed in an external DC magnetic field H0, the frequency v (Hz, or cycles per second) for spin transitions A mg = 1 is... 

X-ray powder diffraction data of the zeolite samples were collected before and after the catalytic reactions with a Diano-XRD 8000 X-ray powder diffraction apparatus. Electron paramagnetic resonance samples were sealed off in quartz tubes on a vacuum line after various treatments and analyzed with a Varian E-3 spectrometer at room temperature. 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

The mass spectrum (MS) of chitin was recorded using a VG Micro-mass 7070 F gas chromatography mass spectrometer imit. The electron paramagnetic resonance (EPR) spectra were recorded using a Varian EPR spectrometer. The MS recorded at a temperature of 300 °C is shown in Eig. 2.22. This temperature was used to obtain a more stable and rich fragmentation pattern. Table 2.13 presents the list of fragments that can be attributed to the ions detected in the recorded mass spectra (MS). 

Spectroscopy. FT-IR spectra were recorded on a Nicolet F-730 spectrometer equipped with an in-situ flow-cell. Electron Paramagnetic Resonance (EPR) spectra were recorded in X-band with a Bruker ESP-300 with a fE (,4 cavity. Diffuse Reflectance Spectroscopy (DRS) spectra were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR. Molecular graphics analysis was done with Hyperchem 3.0 for Windows (Hypercube Inc.). 

X-ray photoelectron spectroscopy (XPS) analyses were performed in a VG Scientific spectrometer and sensitivity factors of 4.0 for Cu 2p3/2 and 1.1 for Zr 3ds/2 were used. Electron paramagnetic resonance (EPR) analyses were performed with a modified Varian E-4 X-band spectrometer. Temperature programmed reduction (TPR) was performed in the tubular flow reactor using 5% H2 in argon as the reductant. 

We said earlier that we can never prove a mechanism—only disprove it. Unfortunately, just as the correct mechanism seems to be found, there are some observations that make us doubt this mechanism. In Chapter 37 you saw how a technique called electron spin resonance (ESR) (or electron paramagnetic resonance, EPR) detects radicals and gives some information about their structure. When the Cannizzaro reaction was carried out with benzaldehyde and a number of substituted benzaldehydes in an ESR spectrometer, a radical was detected. For each aldehyde used, the ESR spectrum proved to be identical to that formed when the aldehyde was reduced using sodium metal. The radical formed was the radical anion of the aldehyde. 

Electron paramagnetic resonance (EPR) studies in a conventional X-band spectrometer showed the following ... 

ELECTRON PARAMAGNETIC RESONANCE NUCLEAR MAGNETIC resonance). Instruments for obtaining spectra of particle beams are also called spectrometers (see spectrum photo-electron spectroscopy). 

The electron paramagnetic resonance spectroscopy measurements were performed in air with the PP/MWCNT (10 wt%) samples using a Mini-EPR SPIn Co. Ltd spectrometer with 100 kHz field modulation. The g factor and EPR intensity (X-band) were measured with respect to a standard calibrating sample of Mtf + and ultramarine. 

Two types of EPR (electron paramagnetic resonance) detectable bistability have been detected during recent years. The first is related to the EPR spectrometer itself and not to the sample. The physical cause of the phenomenon is the non-linear behaviour of the sample to cavity coupling [26]. The width of the hysteresis loop was found to vary with the filling factor of the cavity. This type was detected by Giordano et al. [26] during studies on polypyrrole radical. 

To understand the nature of the spins in the polymers, electron paramagnetic resonance (EPR) experiments were carried out using a Bruker ESP 300 spectrometer equipped with a rectangular cavity that has a TE102 mode fi-equency of 9.5 GHz (X band). An ESR-900 continuous flow He cryostat from Oxford Instruments provided temperature control from 4 to 300 K. 

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