Decoupler field strength

We saw in Section 2-4k that (i) NMR spectra are usually recorded with WALTZ proton decoupling for spectrometers whose field strengths are 9.4 T or above (or whose H frequencies are 400 MHz and above) and (ii) one of the components of WALTZ decoupling, the decoupler field strength yB2, has to be determined for each individual spectrometer. The quantity 762 is a function of both the decoupler power level and characteristics of the probe. In addition, 7 2 depend on the sample itself if highly ionic solutions are being ex- 

In the off-resonance decoupling method, the residual carbon-hydrogen coupling constant Jj-es of the methylene group of dioxane is measured. Two sequential, off (proton)-resonance experiments are performed, one with the decoupler situated at a higher frequency than the chemical shift of the methylene protons and a second with the decoupler located at 

The decoupler modulation frequency employed in WALTZ decoupling is 4(752)- 

2-2 (a) How many data points are required to describe a spec- 

2-3 What is the difference in the amounts of signal acquired for the following two experiments (a) four 90° pulses with a 3-s delay time between pulses and (b) twelve 30° pulses with no delay time between pulses Assume in both cases that rp = 1 s and that relaxation is complete by the time the next pulse is delivered. 

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The left-hand side of the equation can be regarded as the decoupler field strength in units of hertz. This is the same as describing the main magnetic held, B0, as y BJln in hertz. For... 

Figure 7 Decoupling performance of WURST waveform. A Si-H coupling of 7 Hz in hexamethyldisiloxane has been decoupled over 45 kHz-wide band using O.S6kHz of the average decoupling field strength...

Figure 3.56. Calibration of the homonuclear decoupling field strength via the Bloch-Siegert shift. The decoupler offset from the unperturbed resonance was 47.5 Hz causing a shift of 5.5 Hz, indicating the mean if field to be 23 Hz.

Figure 3.69. Calibration of the heteronuclear decoupler field strength via off-resonance proton decoupling. From the reduced splitting of the C- H doublet, the proton rf field strength is calculated to be 2.2 kHz, a typical value for broadband proton decoupling.

The experimental lineshapes of the carboxyl and methyl carbon resonances of fully enriched L-Alanine have been studied in detail at different MAS frequencies and decoupling field strengths. Complex lineshapes at intermediate spinning speeds were explained by the joint effect of off rotational resonance and coherent CSA-dipolar cross-correlation. It was found that coherent CS A-dipolar cross-correlation introduces either a differential intensity and/or a differential broadening of the lines of the J-multiplet. The conditions that lead to such effects were explained and experimentally verified. Additional simulations showed that these effects can be expected over a wide range of static magnetic fields and are not restricted to L-Alanine. 

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