CODEX correlation time

The pointed brackets indicate the powder average, which also contains the effect of the correlation time rc and mixing time /, . It can be shown that the dephasing is independent of the spinning speed and only depends on the total time Ntr.20 Owing to this cor independence, the CODEX pulse sequence works up to very high spinning speeds (see below). 

Formally, when the exchange intensity Hgure 13(b) is plotted as 1 - (tmix NtR)/ it is identical to an orientation autocorrelation function of the process. In the case of CODEX, the recoupling (encoding) time NIr determines the angular sensitivity ((S is the anisotropy parameter of the chemical shift tensor), and the exact mathematics is somewhat involved due to the MAS. In case of static stimulated-echo experiments mentioned above, one obtains essentially analogous, but a mathematically even simpler signal function, that is, the sine-sine correlation function of P2,... 

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