Echo or antiecho optimization with MQMAS sequence in solid-state MAS NMR using a JDK1.3 applet




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Example 2 of MQMAS simulation

The example, which is complementary to Example 1, also deals with the central-transition echo amplitude of a spin I = 3/2 in a powder sample rotating at the magic angle with a rotor speed of 10 kHz.

The strength of the RF magnetic field is 100 kHz.

The values of the two quadrupole parameters are 1000 kHz for the quadrupole coupling constant QCC and 0 for the asymmetry parameter eta.

The simulation associated with the MQMAS sequence is A()B(p2), where the second-pulse length p2 increases from 0 to 10 s by 0.25 s step; the first-pulse length p1 is 6 s. There is no interpulse delay (tau1 = 0, this is an approximation) whereas experimental tau1 is about 10 s.

The pulse length to pulse increment ratios are integers.

The number of integration steps for alpha and for beta Euler angles are MaxAlpha = 20, that for gamma Euler angle is MaxGamma = 10.

The first pulse excites the -3-quantum coherence only.

 

IMAGE: Effect of the second-pulse length on the echo amplitude

The sign of the central-transition echo amplitude also does not change for a long range of the second-pulse length p2 as in Example 1. This curve differs a lot with that obtained in Example 2 of two-pulse MAS simulation.

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