Relaxation studies in the presence of off-resonance rf irradiation


Aim: The classical way to see relaxation in liquids is strongly associated to Bloch’s equations, characterized by a longitudinal T1 and a transverse T2. This obviously needs to be extended in a first step to dipolar cross relaxation as explored by NOESY or ROESY experiments and in a further step to any mechanism involving cross-correlation induced relaxation. What we have studied for a while has led to the definition of a general unified view which links longitudinal relaxation along the static magnetic field direction and transverse one performed in the presence of rf irradiation.


Principle: The key point consists in applying the rf irradiation of amplitude w1 not on-resonance as usual but off-resonance at a distance D in Hz from the spectrum centre. In the frame rotating at the rf field frequency this defines an effective field and we can study the relaxation along this field. This effective field makes an angle q=atan(w1/D)  with the static magnetic field direction and its amplitude W is defined by W2= w12+D2.


Definition and amplitude of the effective field.
The magnetic fields are drawn in a frame rotating at the rf frequency.




Domain of motions which can be studied by relaxation in the presence of off-resonance rf irradiation.



Steady-state or transient measurements:




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