14N Pulsed nuclear quadrupole resonance. 4. Two-pulse sequences for the determination of T1 and T2 relaxation times.

Daniel Canet (1) , Maude Ferrari (1)

1 CRM2 - Cristallographie, Résonance Magnétique et Modélisations

A general theory, based on density matrix calculations, has been developed for the special case of a two-pulse sequence applied to spin 1 (14N) Nuclear Quadrupole Resonance (NQR) of a powder sample. It is shown that the homologous of the NMR inversion-recovery experiment leads easily to the longitudinal relaxation time (associated with the diagonal elements of the density matrix) provided that an appropriate phase cycling is used. Conversely, in spite of two-step phase cycling schemes adapted to transverse relaxation measurements, the homologous of the NMR Hahn spin-echo sequence may pose some problems if the results are displayed in the magnitude mode. First, at short decay times, the echo may be corrupted by unwanted signals. Secondly, in that case, the amplitude of the resulting signal can evolve unexpectedly and differently as a function of the phase of the second pulse. Thirdly, at long decay times, the echo maximum occurs earlier than expected. All these problems in principle disappear with a complete four-step phase cycling scheme and the echo decay curve yields reliably the transverse relaxation time (associated with off-diagonal elements). This theory allowed us to exploit many test experiments performed at different frequencies on hexamethylenetetramine (HMT) and sodium nitrite.

Mots clés: Physical Sciences

Daniel Canet, Maude Ferrari. 14N Pulsed nuclear quadrupole resonance. 4. Two-pulse sequences for the determination of T1 and T2 relaxation times.. Molecular Physics, 2009, 107 (22), pp.2419-2430. ⟨10.1080/00268970903352327⟩. ⟨hal-00530831⟩