Spin-echo pulse

All imaging experiments used the two-pulse spin-echo sequence a-T-2a-t-echo. In 3H experiments, a = 90 ° was used. For 2D 1H M RI of liquids, a 2-mm thick axial... 

R. Siegel, T. T. Nakashima and R. E. Wasylishen, Signal-to-noise enhancement of NMR spectra of solids using multiple-pulse spin-echo experiments. Concepts Magn. Reson., 2005, 26A, 62-77. 

An alternative NMR method has been to use pulsed spin-echo techniques with hydrocarbon adsorbates highly enriched in l3C. Those surface species that have l3C—l3C bonds give rise to modulated free-induction decays (FIDs), which depend on direct l3C/l3C dipolar coupling. The analysis of the modulation provides information about the C—C distances present. C, species or C2 species with l3C —l2C bonds give unmodulated FID components. Furthermore, double... 

D. The Narrow Gradient Pulse Spin-Echo Experiment... 

The Co particles were synthesized by the chemical deposition techniques from C0SO4 7 H2O solutions. The samples were characterized by TEM, X-Ray spectrometry and diffractometiy (DRON - SEIFERT-RM4). For investigation of nearest topological and chemical neighboring of Co atoms the NMR technique was used. The NMR spectra were measured by standard pulse spin-echo... 

CW experiments (sometimes called stationary or steady state ) are ones in which either no modulations are used, or they are so low in frequency that no spectral complications ensue. (This is only approximately the case if 100 kHz field modulation is employed. This frequency gives rise to modulation sidebands and, under saturating conditions, rapid passage effects.) Time-domain ESR involves monitoring the spin system response as a function of time. Pulse ESR can be divided into two broad categories the response of spin systems to sequences of microwave pulses (spin echo) and the response of spin systems to step changes in resonance conditions (saturation recovery). 

Figure 11 shows diagrammatically (Muller and Bloom, 1960) the arrangement of echoes and pulses which occur in a general type of three-pulse spin-echo experiment. In this diagram a pulse of duration 0 to t0 rotates the magnetization by the angle nj2. This pulse is followed by the free induction decay with time constant T determined by both extrinsic and intrinsic relaxation forces. At a time iq (iq > 11 t0) a pulse... 

FlO. 11. Arrangement of echos and pulses in three-pulse spin-echo experiment (Muller and Bloom, 1960). 

Spin echo pulse sequences use a 90° RF pulse followed after half an echo lime (TE) by a 180° RF pulse. Spin-echo signals s decay as ... 

A two-pulse spin echo experiment consists of a 90°-r-180°-r-echo pulse sequence (see Chapter 2.3, Section 2.3.2). The amplitude of the echo is monitored as a function of the time r between the echoes, and the decay time constant is denoted as Jin, the phase memory decay time. J is strongly dependent upon dynamic processes that result in echo dephasing on the time scale of the experiment. In Cu(dtc)2 the coupling of the unpaired electron to the spins of the protons of the ethyl groups is too small to be resolved in the CW spectra. However, when the rate of rotation of the... 

Figure 5 X-band (9.101GHz) two-pulse spin-echo detected absorption spectrum of 2.0 mM Cu(dtc)2 in glassy toluene solution at 30 K, obtained with 20 and 40 ns pulses and a fixed time between the pulses...

Harbridge, J.R., Eaton, S.S., and Eaton, G.R. 2003. Comparison of electron spin relaxation times measured by Carr-Purcell-Meiboom-Gill and two-pulse spin-echo sequences. J. Magn. Reson. 164 44-53. 

Analysis of the dephasing of the out-of-phase echo for radical pairs produced by photo-excitation can give the interspin distance. This technique has been applied predominantly in studies related to photosynthesis. Following creation of the radical pair, a two-pulse spin echo is created. Crucial to the interpretation is that there is phase coherence between eigenstates present in the photo-induced spin-correlated radical pair (84). The spin-spin interaction causes deep modulation in the out-of-phase echo, whereas the normal, in-phase, echo vanishes (84). Distances in the range of 25 - 34 A have been measured to define distances between donor and acceptors in the photosystem (84-96). 

The pulsed (field) gradient-spin echo (PFGSE or PGSE) experiment is used to measure translational diffusion constants [29] (which must not be confused with spin diffusion). It is based on the two-pulse spin-echo experiment (Fig. 12 Sec.II.E.l), with the addition of two field-gradient periods to create a spatial frame of reference in the x and y dimensions. The first gradient is applied between the two pulses the second, between the 180°... 

In addition to the two-pulse spin echo illustrated in Eig. 9, more-complicated pulse sequences are now being routinely used. In a three-pulse sequence, the second 180° pulse in a two-pulse sequence is split into two 90° pulses separated by time T. Then the first experimentally controllable interpulse time r can be adjusted so as to eliminate one nuclear modulation while the second interpulse time... 

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