Excitation of multiple quantum coherences by a single nonselective radiofrequency pulse due to the breakdown of the high-field approximation

Multiple quantum coherences are created by a single nonselective pulse from the equilibrium density matrix when the high-field approximation breaks down. In this situation the equilibrium density matrix also contains bilinear spin operators. In the case of a two spin system having scalar as well as dipolar coupling, both double and zero quantum coherences are excited whereas in the presence of scalar coupling alone, only the zero quantum coherence is created, with no double quantum coherence. Flip angle dependence of the multiple quantum coherences is discussed.