Double quantum coherence of quadrupolar I = 1 nuclei: 14N in NH4ClO4

We have calculated optimal conditions for observing the double quantum coherence of quadrupolar nuclei I = 1 in single crystals and powders after the two and three pulse sequences (theta1)x-tau1-(theta2)alpha-tau2 [-(theta3)beta-tau3] Here alpha and beta are the phase-cycling angles, which were incremented properly to select the desired coherence transfer pathways. Experiments for double quantum excitation and detection were performed on the single crystal and powder samples of NH4ClO4. Because of a fast decay of the signal from the powder after the two-pulse sequence, we employed the third pulse to produce an echo related to the double quantum coherence.