Proton double quantum coherence and cross-relaxation in (NH4)(2)SnBr6

A proton double quantum coherence signal can be observed exclusively from t he T species NH4 groups (with the total spin I = 1 in ammonium compounds at low temperatures by the three-pulse sequence 90 degrees(x) - t(pr) - 90 de grees(x) - t(ev) - 90 degrees(x) - t(a),where t(pr) and t(a) are of the mag nitude of the inverse line width and t(ev) very short. The usefulness of th is pulse sequence, preceded by the additional pulse sequence 90 degrees(x) - t(1) - 90 degrees(-x) - t(2) for creating an unbalance between the A and T species magnetizations, by applying it to cross-relaxation studies in (NH 4)(2)SnBr6. (C) 1998 Elsevier Science B.V. All rights reserved.