Double-quantum-filtered intermolecular single-quantum coherences in nuclear magnetic resonance spectroscopy and imaging

Based on the double-quantum-filtered technique, a three-pulse sequence was designed to effectively eliminate contamination of residual conventional single-quantum coherences (SQC) from intermolecular SQC signals in single-resonance spin-1/2 samples such as water. Analytical expressions were derived from the modified Bloch equations with dipolar fields. All experimental observations and numerical simulation results are in excellent agreement with the theoretical predictions. Compared to the CRAZED sequence, the sequence can effectively suppress residual conventional SQC signals even with great imperfection of radio-frequency pulse flip angles. For the first time, signals from pure intermolecular SQCs were selectively observed in forms of spectrum or image.