Effective Hamiltonian and Polarization Transfer in dipolar coupled Quadrupolar spin-systems.
Physics
We investigate in detail the underlying spin-dynamics associated with time-dependent Hamiltonians by developing theoretical models in complex spin systems (1H-14N, 1H-35Cl etc.). In a recent work, published in Journal of Magnetic Resonance we employed matrix logarithm and Floquet theory to compute numerically the effective Hamiltonian associated to a time-dependent problem in solid state Nuclear Magnetic Resonance, Cross-Polarization under fast Magic Angle Spinning (MAS) and Double Cross Polarization under fast MAS. A detailed analytical solution of the associated time-dependent problem is challenging due to the interference between large 14N time-dependent quadrupolar interaction and 14N RF irradiation. The structure of the effective Hamiltonian was found to exhibit a strong dependence on crystallite orientation, with several spin terms of comparable magnitude present for most crystallite orientations. A comprehensive insight on 1H-14N CPMAS and double CP spin dynamics was presented through numerical simulations, and the observations are substantiated with analytical derivations
Figure:- CP-MAS signals arising from a powder showing Destructive interference and Double CP MAS signals showing constructive interference. Matching conditions for CP transfer is shown below.
Ref: "Effective Hamiltonian and 1H-14N cross polarization/double cross polarization at fast MAS"; J. Magn. Reson., 320, 106832, 2020; Sadasivan V. Sajith, Sundaresan Jayanthi, Adonis Lupulescu