Delays alternating with nutation for tailored excitation sequence

The excitation profile of multiple bands was also known for periodic RF pulses, such as the DANTE (delays alternating with nutation for tailored excitation) sequence.26 Similar to the PIP, all the phases and strengths of the effective RF fields can be obtained by expanding the periodic pulse into a Fourier series and properly rearranging the terms afterwards.27 Detailed calculation, comparison with the PIP, and the excitation profiles by a periodic pulse of fix sin(7tt/T) Ix and a DANTE sequence are presented in Section 3. 

To generate an exchange curve, one of the two resonances involved must be inverted selectively. By whichever technique a selective inversion is carried out, it is important that the other resonances not be perturbed. The most frequently used inversion techniques in RR experiments are a long, soft pulse or an asynchronous DANTE (delays alternating with nutation for tailored excitation) sequence. 

In some spectrometers it is not feasible to generate BURP or related tailored soft pulses. A useful alternative is the DANTE pulse sequence (delays alternating with nutation for tailored excitation). Normal high excitation power is used, but rather than apply a single 90° pulse, the DANTE method uses a sequence of small angle pulses that sum to 90° but with a short time between pulses during which nuclei... 

An alternative solution to the problem of selectively observing, for example, the H NMR spectrum of a metal-hydride in protio-, rather than deutero-solvent is to excite just that region of the NMR spectrum that contains signals of interest. This can be done using a shaped soft pulse, using a DANTE (delays alternating with nutation for tailored excitation) type sequence or, on a modem... 

An early alternative to soft pulses was the DANTE Delays Alternating with Nutation for Tailored Excitation) experiment, which used a sequence of short, hard pulses of angle a <3C 90°, followed by a fixed delay t to achieve selective excitation. Thus, the pulse sequence is (a-T), ]. Nuclei that are on resonance are eventually driven to the y axis and hence are selected, whereas those more removed from the frequency range are not affected. The sequence of hard pulses can achieve a result similar to that of soft pulses and even can be shaped by modulating the duration of the pulse lengths, but DANTE pulses lead to spectral artifacts not created by soft pulses, such as unwanted sidebands. 

Selective excitation was accomplished by using a delays alternating with nutations for tailored excitation (DANTE) sequence of 20 short rf pulses of x =0.6 is duration [4]. The pulse separation used was 20 ps resulting in the total duration of the DANTE sequence of x,=400 [iS and the corresponding spectral excitation width A of the center band of 2.5 kHz. The excitation sidebands were separated from the centerband by (Xp) = 50 kHz and did not affect the NMR spectrum. After a recovery period,x of at least 35 ps a final 90° pulse was applied followed by the detection of the free induction decay. 

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