Understanding NMR Spectroscopy phần 10 pdf

... sufficient?] E9 -10. Use the formula given in section 9.6.2 for the overall decay of magnetization during a gradient 2 γ Gtr max to calculate how long a gradient is needed to dephase magnetization to (a) 10% and ... 10% and (b) 1% of its initial value assuming that: G = 0.1 T m –1 (10 G cm –1 ), r max = 0.005 m (0.5 cm) and γ = 2.8 × 10 8 rad s –1 . [Put all the quantities in SI u...

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... energy levels” c  James Keeler, 2002 Understanding NMR Spectroscopy James Keeler University of Cambridge, Department of Chemistry c  James Keeler, 2002 2 10 NMR and energy levels ααα αβα ββα βαα 1 23 4 ααβ αββ βββ βαβ 5 67 8 Fig. ... NMR. This model has its limita- tions, but it is very useful for understanding how pulses excite NMR signals. We can also use the vector model to...

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... way, 3.11 Off-resonance effects and soft pulses 3–17 (a) (b) (c) -20 -10 10 20 -1 -0.5 0.5 1 -20 -10 0 10 20 0.5 1 -20 -10 10 20 -1 -0.5 0.5 1 M x M y M abs Ω / ω 1 Ω / ω 1 Ω / ω 1 Fig. 3.26 Plots ... = π/2 and the duration, t p is 12 × 10 −6 s; therefore ω 1 = π/2 12 × 10 −6 = 1.3 10 5 rad s −1 . The maximum offset is 2500 Hz, which is 2π × 2500 = 1.6 × 10 4 rad s −1 . We see tha...

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... example, such a correction by 100 ◦ means that the phase correction is zero in the middle (at zero offset) and rises linearly to +100 ◦ at on edge and falls linearly to 100 ◦ at the opposite edge. For ... the max- imum offset is about 100 ppm which translates to 12500 Hz. Let us suppose that the 90 ◦ pulse width is 15 µs, then the phase error is 2π × 12500 × 15 × 10 −6 ≈ 1.2radians whi...

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... three bits the output of the ADC could take just 8 values: the binary numbers 000, 001, 010, 011, 100 , 101 , 110 and 111. The smallest number is 0 and the largest number is decimal 7 (the total number ... output power is P out the attenuation in dB is 10 × log 10 P out P in ; note that the logarithm is to the base 10, not the natural logarithm. The factor of 10 is the “deci” part i...

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... represented as the corresponding operator, I z . Likewise for the S-spin magnetization Snnnn z =−+− 1234 [10] A third combination of populations will be needed, which is represented by the operator 2I z S z 2 132 ... difference in population differences across the two I-spin transitions; likewise, comparison with Eq. [10] shows that the same operator also represents the difference in popula...

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... uses coherence transfer pathways to specify the desired outcome of the experiment. 9.2 Phase in NMR In NMR we have control over both the phase of the pulses and the receiver phase. The effect of ... Coherence Selection: Phase Cycling and Gradient Pulses † 9.1 Introduction The pulse sequence used in an NMR experiment is carefully designed to produce a particular outcome. For example, we...

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... the 180° pulse. 9.2.8 Difference spectroscopy Often a simple two step sequence suffices to cancel unwanted magnetization; essentially this is a form of difference spectroscopy. The idea is well ... pulse phase phase shift experienced by transfer with ∆p = –3 equivalent phase 10 0 0 2 90 270 270 3 180 540 180 4 270 810 90 The fourth column, labelled "equivalent phase", is just...

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... for water, which is 2.1 × 10 –9 m 2 s –1 at ambient temperatures. c Diffusion constant taken as 0.46 × 10 –9 m 2 s –1 . d Diffusion constant taken as 0.12 × 10 –9 m 2 s –1 . 9.6.6.1 ... gradient pulse pair of 2 ms duration and of strength 10 G cm –1 for a small, medium and large sized molecule; data is given for ∆ = 2 ms and ∆ = 100 ms. It is seen that even for the mo...

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