Abstract: For normal organic solids,the heteronuclear dipolar interaction between the directly bonded S and I spins is stronger than the I-I coupling between the SI_n groups and the other protons.As a result,the interactions in the SI_n subsystem dominates the spin dynamics of the cross polarizatinn (CP) process.In the light of this new concept,theoretital studies and technical developments of polarization transfer under magic angle spinning (MAS) have leaped forward.Especially,a variety of new techniques have emerged to enbance the polarization transfer efficiency at high MAS speeds.The common feature of these approacbes is to modulate the phases or amplitudes of the radio frequency irradiations,while keeping the high MAS speeds unchanged.A series of spectral editing methods have been developed,which can generete four subspectra according to the proton multiplidties,i.e.the nonprotonated-C,methine,methylene,and methyl subspectra.This technique has been applied to a set of coal samples,where four types of signals orerlap completely in the normal CPMAS spectrum,and has yielded encouraging results.

Key words: Cross polarization/magic angle spinning (CPMAS), Polarization Transfer (PT), Spectral editing