Spin counting and decoherence during dipolar evolution in a liquid crystal

A.K. CHATTAH; AGUSTÍN GÓMEZ; H.M. PASTAWSKI; P.R. LEVSTEIN

Miami

Conferencia; 53nd ENC (Experimental Nuclear Magnetic Resonance Conference); 2012

ENC

In this work we present multiple quantum solid state NMR experiments to study the many-body proton dynamics in liquid crystal MBBA. The usual pulse sequence with evolution, mixing and detection have been used where the spin dynamics is governed by the dipolar Hamiltonian (H0xx). Initially the system is in equilibrium with the Zeeman field and a rotation around the z axis encodes the multiple quantum coherence orders in the Zeeman basis after the dipolar evolution during a time t. A spin-lock r.f. field is used during mixing (2*tau) to generate a reverted dynamics (- H0xx/2). A Loschmidt Echo (LE), obtained by measuring the signal after H0xx and (-H0xx), allows to give conclusions on the intrinsic decoherence of the system and to set the experimental conditions. Using 1H-1H interactions obtained from these experiments, simulations of the spin dynamics have been performed. Comparison between LE obtained from local (I1z), or global (Iz) initial conditions will be discussed.