Behavior of two almost identical spins during the CPMG pulse sequence.
Multiple-spin-echo experiments have found wide use in nuclear magnetic resonance spectroscopy. In particular, the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is used to determine transverse relaxation times T(2). Herein it is demonstrated, both theoretically and experimentally, that for a pair of almost identical spins-1/2 the experimental setup can have a profound effect on the observed spin dynamics. It is shown that, in the case of dipolar relaxation, the measured T(2) values can roughly vary between the limits of identical and unlike spins, just depending on the repetition rate of pi pulses with respect to chemical shift separation. Such an effect can, in the extreme narrowing regime, amount to a 50% difference.
Tosner
Zdenek
Z
Department of Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 128 43 Prague 1, Czech Republic. tosner@natur.cuni.cz
Skoch
Antonín
A
Kowalewski
Jozef
J
D004578:Electron Spin Resonance Spectroscopy