Pulse phases

Most NMR experiments use combinations of two or more of the four pulse phases shown in Fig. 1.42. The phase of the pulse is represented by the subscript after the pulse angle. Thus, a 90f, pulse would be a pulse in which the pulse angle is 90° and -y is its phase (i.e., it is applied in the direction —y to +y), so it will cause the magnetization to rotate about the y-axis in the xz-plane. 

Scan Pulse Sign A Sign B Receiver phase code Receiver mode Pulse phase A B... 

Table 3.7.1 Rf pulse phases (in degrees) for the DDIF experiment.

Figure 22 Pulse sequence of the HMBC-RELAY experiment. Filled and open bars represent 90° and 180° pulses, respectively. All other phases are set as x, excepted otherwise stated. A two-phase cycle x, —x is used for the pulse phases (j>, and

Figure 36 Pulse sequences for the CBC-HSQMBC experiment. Narrow and thick bars represent 90° and 180° RF pulses, respectively. Pulse phases are along x unless indicated otherwise. Phase cycles are (pn = x, x

Fig. 5 Radio frequency pulse sequences for measurements of Sj and Si in DSQ-REDOR experiments. The MAS period rR is 100 ps. XY represents a train of 15N n pulses with XY-16 phase patterns [98]. TPPM represents two-pulse phase modulation [99]. In these experiments, M = Nt 4, N2+ N3 = 48, and N2 is incremented from 0 to 48 to produce effective dephasing times from 0 to 9.6 ms. Signals arising from intraresidue 15N-13C DSQ coherence (Si) are selected by standard phase cycling. Signal decay due to the pulse imperfection of 15N pulses is estimated by S2. Decay due to the intermolecular 15N-I3C dipole-dipole couplings is calculated as Si(N2)/S2(N2). The phase cycling scheme can be found in the original figure and caption. (Figure and caption adapted from [45])...

Siegel et al. showed that enhancement of the CT can also be obtained using hyperbolic secant (HS) pulses to invert selectively the STs [74], Unlike the DFS waveform, whose frequency sweep is generated by a constant rf-pulse phase while modulating the amplitude, the HS pulse utilizes both amplitude and phase modulation, yielding an enhancement exceeding that obtained by DFS or RAPT [61, 74, 75]. Most recently, the pulse sequence called wideband uniform-rate smooth truncation (WURST) [76] was introduced to achieve selective adiabatic inversion using a lower power of the rf-field than that required for the HS pulses [77,78]. One of its applications involved more efficient detection of insensitive nuclei, such as 33S [79]. 

Fig. 17.4 Common filter elements a X-half filter based on X pulse phase cycling [16, 17], b X-half filter with purge gradient [18], c X-half filter as in a, but with refocusing period for the hetero-nuclear antiphase magnetization [16, 17]. Sequences d [22], e [23] and f [18] show double filters based on single filter elements the delays r and r can be set to slightly different values to cover a broader range of ]J coupling constants (see text for a more detailed description).

Fig. 21.1 Pulse sequence to selectively observe solvent-exposed amide protons with TROSY (SEA-TROSY). Narrow and thin bars represent 90 and 180° rf pulses, respectively. Unless specified otherwise, pulse phases are along the x axis. The pulsed field gradients are of 500 ms duration with strengths of gi =20 G cm-1, g2 = 30 G errf1, g3 = 40 G errf1, g"4 = 15 G cm-1, g5 = 55 G errf1. The bipolar gradient gj is 0.5 G errf1 and is used to avoid...

Proton-proton homonuclear decoupling has been performed by the ESLG decoupling sequence [46]. Quadrature detection in coj was achieved by using the time proportional phase increment method (TPPI) [47]. During the acquisition period, two pulse phase modulation (TPPM) heteronuclear decouphng ]48] was applied (Figure 7.6). 

Pulse sequence for MAS NMR. A) CFMAS. B) CPNAS with TOSS. T is magnetization transfer A, acquisition X,Y, -X are pulse phases and represents a delay. 

Quadrature images in the Fi dimension can be suppressed by expanding the 8-step phase cycle to 32 steps or 16 steps, respectively, using CYCLOPS [20] or 2-step CYCLOPS [21]. In the CYCLOPS scheme, the phases of all pulses are simultaneously incremented by 90°, 180° and 270°. In the 2-step CYCLOPS scheme, the incrementation of the pulse phases is limited to the 90° step. 

Solid-state C variable-amplitude cross polarization magic-angle spinning (VACP/MAS) nuclear magnetic resonance (NMR) spectra were acquired for the sorbitol samples. Proton decoupling was achieved by a two-pulse phase modulation (TPPM) sequence. Identical C spectra were measured for the y-form sorbitol samples, and a representative spectrum is shown in Figure 9. 

Lim, S. H., Caster, A. G., and Leone, S. R. 2005. Single-pulse phase-control interferometric coherent anti-Stokes Raman scattering spectroscopy. Phys. Rev. A 72(4) 041803. 

Oron, D., Dudovich, N., and Silberberg, Y. 2002. Single-pulse phase-contrast nonlinear Raman spectroscopy. Phys. Rev. Lett. 89(27) 273001. 

Fig. 2. Pulse scheme for the gradient-selected, sensitivity-enhanced X/Y se-HSQC experiment as employed for 31P/15N correlation spectroscopy in Ref. 25. 90° and 180° hard pulses are denoted by solid and open bars, respectively. 2 are delays of length 1/(4 /x,y)> and is a short delay of the same length as the gradient pulse (typically rj 1 ms). Pulse phases are x, unless specified. The ratio of gradient pulse strengths is set to G2/Gi = Yy/Yx, and quadrature detection in Fi is achieved by recording every transient twice and changing the sign of G2 in the second scan.

Fig. 4. Modified X/Y IMPEACH-MBC pulse sequence used for 19F/15N shift correlation according to Ref. 27. The notation of 90° and 180° pulses is as before. The (d/2 — 180°(Y) — d/2) element represents a variable delay that is incremented concurrently with the decrementation of the accordion delay vd. Pulse phases are x, unless specified x = — x 2 = x, — x 3 = x, x, — x, — x = , — x, — x, x. The bipolar gradients Gs flanking the 180°(Y) pulse can be set to arbitrary power levels, and the relative strengths of the coherence selection gradients G and G2 are determined by G2/G1 =2 Yy/Tx-...

Recently, Silberberg and coworkers have introduced a different approach for active phase control in CARS [44 47]. By tailoring the spectral phase of a single ultrashort laser pulse, phase-sensitive detection of the resonant signal has been demonstrated where the strong nonresonant CARS background of... 

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