Hahn single spin

Hence, in the idealized zero-quantum coupling topologies that are characteristic for most Hartmann-Hahn-type experiments, the magnetization-transfer functions between two single spins 1/2 are independent of the direction of the transfer (Griesinger et al., 1987a). 

Only recently, new multiple-pulse sequences that were developed specifically for broadband heteronuclear Hartmann-Hahn experiments in liquids were reported. The SHR-1 sequence developed by Sunitha Bai et al. (1994) consists of a windowless phase-alternated composite pulse R, which is expanded according to the MLEV-8 supercycle. R was optimized based on a phase-distortionless single-spin 180° composite pulse and is related to the composite pulses used in DIPSI-1 (Shaka et al., 1988) and the composite pulses in the homonuclear IICT-1 sequence (Sunitha Bai and Ramachandran, 1993). The bandwidth of the SHR-1 sequence is comparable to the bandwidth of DIPSI-3, albeit with a slightly reduced transfer efficiency (Sunitha Bai et al., 1994 Fig. 33F). 

As increasing the time interval between the single-shot DNP operation and the aH NMR measurement, the intensity of the magic echo was found to decrease. Instead, the intensity of the 1H Hahn echo grew up, as demonstrated in Figure 19B-D). The fact that the inhomogeneous character in the aH spectra increased with time shows that the spin polarization had been transferred to the place where the H spins were dilute, that is surrounded by the 2H spins in the heavily deuterated host material. 

NMR. The CP/MAS spectra were obtained on a single coil, double-tuned probe similar in design to that reported earlier (15) but modified (16) for the electromagnet of the Varian XL-100-15 system. A homebuilt receiver system allows single coil operation. The probe uses a D2O external lock and a special rotor and stator assembly design to provide MAS. The carbon-13 (25.16 MHz) and the proton (100.06 MHz) radio frequency fields are 17 G and 12 G, respectively for 90 watts of power. The H spin locking pulse of 90° may be varied in terms of length and amplitude while the amplitude of the - C irradiation can be controlled to within 0.1 db to match the Hartmann-Hahn (17) condition. The isolation between the two channels is in excess of... 

N, or 29Si. In CP, both nuclear spin species are spin locked and the rf amplitudes adjusted so that their Larmor precession frequencies in their respective rotating frames are equal the Hartmann-Hahn condition. The single-contact CP enhancement of the rare spins is given by yj/ys. Additional enhancement normally occurs because the CP experiment may be recycled at a rate limited by the usually much faster spin-lattice relaxation rate of protons rather than that of the rare spins. 

The CP/MAS spectra were taken with the single contact (6) sequence. The 90° pulse for the H spin locking is continuously variable and the amplitude of the 13C irradiation controlled to within 0.1 db for matching the Hartmann-Hahn (7) condition. 

Although in general, only one multiple-pulse sequence is applied to homonuclear spin systems, it can be useful to apply different multiple-pulse sequences to several nuclear species at the same time by using separate rf channels. In heteronuclear Hartmann-Hahn experiments, the same multiple-pulse sequence is usually applied simultaneously to two or more nuclear species. However, some selective homonuclear Hartmann-Hahn experiments are also based on the simultaneous irradiation of a multiple-pulse sequence at two or more different frequencies (see Section X). If only a single homonuclear rf channel is used, this can be achieved experimentally by adding an amplitude or phase modulation to the sequence, in order to create appropriate irradiation sidebands (Konrat... 

In a system consisting of two coupled spins 1/2, Hartmann-Hahn transfer can be conveniently analyzed based on the one-to-one correspondence between the evolution of the density operator in the zero-quantum space that is spanned by the operators (ZQ),, (ZQ)y, and (ZQ) [Eq. (14)] and the magnetization trajectory of a single, uncoupled spin in the usual rotating frame (Muller and Ernst, 1979 Chingas et al., 1981 Kadkhokaei et al., 1991 see Fig. 2). This equivalence can be used for the construction of zero-quantum analogs of well-known composite pulses. Effective phase shifts of the zero-quantum field can be implemented by short periods of precession about the z axis of the zero-quantum frame... 

The enhancement of the population difference across the CT leads to an enhancement of the spectral intensity of a static or MAS experiment of half-integer quadrupolar spins with either a single 90° pulse experiment or a Hahn-echo experiment preceded by a FAM block. " The schematic of the former is shown in Fig. 23b. 

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