Ultra-broadband Heteronuclear Hartmann-Hahn polarization transfer
  It is showed on the basis of the multiple-quantum operator algebra space formalism that ultra-broadband heteronuclear Hartmann-Hahn polarization transfer could be achieved by the amplitude- and frequency-modulation quasi-adiabatic excitation (90 degree) pulses, while it is usually difficult for the adiabatic inversion pulses to achieve effectively broadband Hartmann-Hahn transfer in a heteronuclear coupled two-spin system. The adiabatic and quasi-adiabatic pulses have an important property that within their activation bandwidth flip angle of the pulses is independent of the pulse duration and the bandwidth increases as the pulse duration. This property is importanr for construction of the heteronuclear Hartmann-Hahn transfer sequences with the quasi-adiabatic 90 degree pulses. Theoretic analysis and numerical simulation show that the heteronuclear Hartmann-Hahn transfer is performed in the even-order multiple- quantum operator algebra subspace of the two-spin system. The multiple-quantum operator algebra space formalism may give a powerful guide to the construction of ultra- broadband heteronuclear Hartmann-Hahn transfer sequences with the quasi-adiabatic 90 degree pulses. 
Xijia Miao