Multiple-pulse sequence phase-modulated sequences

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... 

Phase-modulated multiple-pulse sequences with constant rf amplitude form a large class of homonuclear and heteronuclear Hartmann-Hahn sequences. WALTZ-16 (Shaka et al., 1983b) and DIPSI-2 (Shaka et al., 1988) are examples of windowless, phase-alternating Hartmann-Hahn sequences (see Table II). 

The J-modulated spin-echo technique " and the DEPT technique " are pulse sequences, which transform the information of the CH signal multiplicity and of spin-spin coupling into phase relationships (positive and negative amplitudes) of the C signals in the proton decoupled C NMR spectra. The DEPT technique benefits from a polarisation transfer which increases the sensitivity by up to a factor of 4. For... 

The preparation time is designed to place the spins in a specified state, which is most often a relaxation to thermal equilibrium state. The evolution time allows for the phase modulation of the spins by J coupling or other interactions. The evolution time is selected to optimize the information content of the resultant spectra and generally corresponds to the magnitude of the selected interaction, that is, Tg = 1/7 or some multiple depending on the nature of the experiment. The read pulse terminates the sequence and is followed by detection of the FID. 

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