Echo spectra

Fig. 13. Calculated 2H solid echo spectra for log-Gaussian distributions of correlation times of different widths. Note the differences of the line shapes for fully relaxed and partially relaxed spectra. The centre of the distribution of correlation times is given as a normalized exchange rate a0 = 1/3tc. For deuterons in aliphatic C—H bonds the conversion factor is approximately 4.10s sec-1...

The REDOR 13C echo spectra of two different PMA/[l-13C]Leu/[15N]Leu samples are shown in Figure 10. Signals from the enriched carboxyl carbon of leucine are sharp at all concentrations. Apparently, even at the lowest concentration, the leucine molecules are not well dispersed throughout the polymer, but instead are clustered in small, ordered, crystalline-like domains. The doubling of the carboxyl signal is also seen for pure, crystalline leucine and is attributable to the detailed packing of the leucine molecules in the solid state. 

Figure 10. REDOR 13C NMR echo spectra of PA imbibed with equimolar amounts of[l-13C]Leu/[15N]Leu (bottom) 10 1 1, by weight (top) 50 1 1, by weight. Spectra were collected using the pulse sequence of Figure 2 with VR = 3 kHz Nc = 30.

Fig. 4. Neutron spin echo spectra for the self-(above) and pair-(below) correlation functions obtained from PDMS melts at 100 °C. The data are scaled to the Rouse variable. The symbols refer to the same Q-values in both parts of the figure. The solid lines represent the results of a fit with the respective dynamic structure factors. (Reprinted with permission from [41]. Copyright 1989 The American Physical Society, Maryland)...

Fig. 6 (a) SQ and (b) DQ rotor-synchronized 2H MAS NMR spectra of sodium tetrathionate dihydrate-d4 (solid lines). The dashed line in (a) represents the exact numerical simulation of the SQ spectrum for random molecular motion with the rate constant k given in the figure, (c) The corresponding experimental and simulated static 2H quadrupolar-echo spectra, (d) Simulated SQ (solid line) and DQ (dashed line) linewidths as functions of k. (Reproduced with permission from [88])... 

Fig. 3.29 Neutron-spin echo spectra from polyethylene melts of various molecular weights. The Q values correspond to squares Q=0.03 A circles Q=0.05 A triangles (up) Q=0.077 A diamonds Q=0.096 A triangles (down) Q=0.115 A crosses Q=0.15 k Filled symbols refer to a wavelength of the incoming neutrons A=8 A and open symbols refer to A=15 A. For lines, see explanation in text (Reprinted with permission from [71]. Copyright 2002 The American Physical Society)...

Fig. 2. 500 MHz pulsed field gradient stimulated echo spectra of a mixture of choline chloride, acetone and TSP in D2O, obtained using the LED sequence as described in the text. A signal from an unidentified impurity is visible just to high field of the acetone resonance.

Extensive analysis of the EPR and redox behavior of this unusual copper protein led to the hypothesis that the protein might contain a Cu(A) site similar to that in cytochrome oxidase (Riester et ai, 1989) and that the unusual seven-line EPR is due to the Cu(A)-type site. An alternative interpretation of this EPR is based on electron spin-echo spectroscopy as well, and that is that the seven-line EPR is due to a half-met Cu—Cu pair and to unusual type I sites (Jin et ai, 1989). Three sets of spin-echo peaks can be attributed to nitrogens on imidazole ligands to a CuA-type site and to another imidazole on the half-met site. The electron spin-echo spectra of cytochrome oxidase are similar, although there is not enough copper in cytochrome oxidase for a half-met site. Conceivably, the property of delocalization of the paramagnetic electron could be effected by the proposed bridging between Cub and heme as (nomenclature summarized by Capaldi, 1990), which are proposed to be 3-4 A apart. 

Simulations were made for all three frequencies, determining the g-values principally at 94 GHz, and showing transferability of parameters between frequencies. It was demonstrated (from the model compounds) that interfering signals from Mn(II) at 94 GHz could be eliminated using field-swept echo spectra and making use of the different 7) or r2 relaxation times for the components of the spectra. 

Fig. 9. PHBA/BPT - Xydar, molecular motion observed in 2H quadrupole echo spectra (61.4 MHz)...

Fig. 2. Photon echo spectra vs. population time (a, d) and coherence time (b, c, e, 1) at fixed other delay time for pump or probe pulse wavelength at the maximum (575 nm) and on the blue side (560 nm) of the absorption maximum. The inset shows the contour plot of corresponding figure...

Diffusion-ordered spectroscopy (DOSY)45 is a NMR spectroscopic technique that separates the NMR signals of different compounds according to their diffusion coefficient (D, their rate of diffusion in a particular medium). A series of spin echo spectra is measured with different pulsed field gradient strengths, and the signal decays are fitted to give diffusion coefficients for each compound present. In 2D DOSY this... 

Figure 14.3 Deuterium solid-echo spectra of unfilled (a) and filled (b) polyfdimethylsiloxane] networks at 305 K with and without mechanical stress as given by the parameter X [23]. This example demonstrates the sensitivity of the NMR lineshape and thus of the spin interactions to internal and external conditions...

VES requires a tunable source of infrared pulses. In the experiments presented below, vibrational echo spectra were taken using the Stanford FEL employing the same experimental setup used to perform the vibrational echo decay experiments discussed above (16). 

It has been usually argued that the NMR fine-shape reaches the solid-state, rigid-lattice limit at temperatures around Tg (cf. Fig. 38), and consequently no dynamical effects are expected when measuring solid-echo spectra. While such... 

Experimental three pulse electron spin echo spectra of Ag (A) in Lij2 A zeolite. The two large sharper peaks below 1 ps are due to two pulse interference. 

Cu isotopes both with nuclear spin I-3/2. The nucle r g-factors of these two isotopes are sufficiently close that no resolution of the two isotopes is typically seen in zeolite matrices. No Jahn-Teller effects have been observed for Cu2+ in zeolites. The spin-lattice relaxation time of cupric ion is sufficiently long that it can be easily observed by GSR at room temperature and below. Thus cupric ion exchanged zeolites have been extensively studied (5,17-26) by ESR, but ESR alone has not typically given unambiguous information about the water coordination of cupric ion or the specific location of cupric ion in the zeolite lattice. This situation can be substantially improved by using electron spin echo modulation spectrometry. The modulation analysis is carried out as described in the previous sections. The number of coordinated deuterated water molecules is determined from deuterium modulation in three pulse electron spin echo spectra. The location in the zeolite lattice is determined partly from aluminum modulation and more quantitatively from cesium modulation. The symmetry of the various copper species is determined from the water coordination number and the characteristics of the ESR spectra. 

Experimental three pulse electron spin echo spectra of two types of Chi in Na -A zeolite. Chi (( (D-CO-is the dominant copper species in site S2 in freshly prepared, hydrated Nai2 A and Cu +(0z)j(D20)2 in site S2 is the dominant species after partial dehydration under vacuum at room temperature. The different deuterium modulation depths characterize the different numbers of coordinated waters in these two Cu species. 

The influence of hydrophilic Aerosil on the chain dynamics in the adsorption layer becomes evident with the help of comparison of solid-echo spectra for a series of filled PDMS samples containing different amounts of Aerosil as shown in Fig. 3 [21]. 

Fig. 3. Three fully relaxed solid-echo spectra for mixtures of PDMS containing (a) 40 (149 phr), (b) 60 (336 phr), and (c) 89 (1813 phr) vol% of hydrophilic Aerosil (380 g ) [21] spectra containing a very weak broad component are also...

Thus, the H relaxation experiments and the analysis of the solid-echo spectra show that the adsorption of PDMS chain units on the surface of hydrophilic Aerosil significantly restricts the motion of chain tmits adjacent to the filler surface. However, chain units in the adsorption layer are not rigidly linked to the surface of Aerosil at temperatures well above the Tg. Motions of chain units in the adsorption layer become less restricted as the temperature increases. 

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