WAHUHA multiple-pulse sequences

A pioneering work on the WAHUHA multiple-pulse sequence applied to F NMR of a fluorinated polymer was reported by Ellett et al. [116]. They obtained resolved chemical shifts for the OCF3 and CF2 peaks (separation 73 ppm) of a copolymer of 60/40 TFE and perfluoromethylvinyl ether. Good agreement between the area of the peaks and the known composition of the copolymer was obtained. The anisotropy of the chemical shift of the CF2 groups was approximately determined. 

WAHUHA multiple-pulse sequence developed by Waugh, Huber, and Haeberlen... 

At the time of this writing, a rapidly growing area of research within NMR is the high resolution study of solids brought about by the development of certain multiple pulse sequences (such as the WAHUHA and MREV-8) on the one hand and an adaptation of the Hartmann and Hahn cross polarization experiment to obtain spectra of dilute spins on... 

The influence of the line broadening interactions described above (see Sect. 2.1) can be suppressed at least partly by the appHcation of special multiple-pulse sequences [8,13-15]. A typical example is the so-called WAHUHA (Waugh, Huber, Haeberlen) sequence [8] which consists of four "/2-pulses with alternating phases -[-r- nl2)x-2T- nl2) -T-(nl2)y-2r-(nl2).y-]-. This pulse cycle which exhibits a cycle time of t =6ris appHed repeatedly to the resonating spins. Sam-pHng the FID at multiples of leads to a suppression of the influence of the homonuclear magnetic dipole-dipole interaction. It has, however, to be stated... 

The original homonuclear line-narrowing pulse sequence (WAHUHA) [23] was a four-pulse sequence later elaborations involve more pulses in the total cycle and offer compensation for pulse imperfections and/or higher order averaging of the homonuclear dipolar interaction [24]. Currently, the most popular multiple pulse sequences are the eight-pulse MREV-8 sequence [24a] and the 24-pulse BR-24 sequence [24b]. 

WAHUHA, the simplest multiple pulse sequence, is composed of four 90° pulses ... 

Multiple pulse sequences average the dipolar Hamiltonian, but also affect other Hamiltonians to an extent which depends on the particular sequence. For example, the WAHUHA sequence scales chemical shift anisotropies by a factor of l/VS. 

Multiple pulse sequences can also be used to provide effective broad-band decoupling. The original pulse sequence of this kind was the WAHUHA sequence of Waugh and co-workers which was designed to minimize broadening arising from homonuclear dipolar coupling in solid-state spectra. 

Figure 6. The WAHUHA multiple-pulse-cycle sequence for homonuclear dipolar decoupling. The repeated cycle lies between successive vertical dotted lines. The crosses represent typical signal sampling points. The initial pulse P produces transverse magnetisation and x,y,3, y correspond to orthogonal directions in the rotating frame for the pulse phases.

The homonuclear dipolar H- H interactions can be removed by modulating the spin states rather than the spatial factors [19]. This multipulse sequence reduces the line widths in rigid solids from 10 to 10 Hz. The multiple-pulse sequence used is the WAHUHA sequence (after the initials of the originators) and is... 

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