Pulsed Line Narrowing in Nitrogen‐14 NQR

On the basis of the average Hamiltonian theory the possibility of the pulsed narrowing of nitrogen 14 NQR lines in powders is studied theoretically using the fictitious spin‐(l/2) operator formalism. The modified Carr‐Purcell pulse sequence t (τ– t –2τ– t –τ) n is shown to be more acceptable for this purpose. The average Hamiltonians of inhomogeneous broadening and heteronuclear dipole‐dipole interactions as well as the secular part of the Hamiltonian of the interaction of a spin system with torsional oscillations of molecules are proved to commute with the initial density matrix prepared by the first (preparatory) pulse t The experimental curves of the spin echo envelopes in the pulse sequence are given. The decay time constants obtained experimentally at 77 K range between 0.5 s in methylamine and 10 s in sodium nitrite and agree with the spin–lattice relaxation times in these compounds.