Two dimensional NQR separation of inhomogeneous and homogeneous lineshapes in disordered solids

Abstract

A two-dimensional (2D) zero field NQR separation of inhomogeneous and homogeneous lineshapes technique is described. The nuclear spin Hamiltonian for spinsI>1/2 in zero magnetic field consists to a good approximation only of the electric quadrupole term. The 2D separation technique enables a separate spectroscopic observation of a static and a randomly time-fluctuating dynamic part of the quadrupole interaction. The separation is based on the fact that nuclear spin precession under a static quadrupolar Hamiltonian can be time-reversed whereas this can not be achieved under the action of a randomly time-fluctuaing Hamiltonian. The 2D spectrum displays in theω ₂-domain the inhomogeneously broadened lineshape, which is a convolution of the inhomogeneous static frequency distribution function and the homogeneous (adiabatic) lineshape. Theω ₁-domain shows the pure homogeneous lineshape. A deconvolution of the inhomogeneous lineshape with the homogeneous one yields a pure static inhomogeneous frequency distribution function which is characteristic and theoretically known for many different models of disordered solids like glasses and incommensurate systems. This technique is important in studies where both lineshapes have comparable widths. The 2D NQR separation technique has been applied to⁷⁵As in a proton glass Rb_0.98(NH₄)_0.02H₂AsO₄.