Fig. 2.

The four parts of the gsHZQC experiment are depicted as a 2 × 2 grid in which rows denote inversion of the outer multiplet components and columns generate echo/antiecho data. Frequency discrimination is controlled by placing the composite ¹H 180° pulse before or after the t₁ evolution period, while the phase of the outer multiplet components is controlled by placement of the ¹³C 180° pulse. Due to variation in the position of the ¹H and ¹³C 180° pulses, the encode gradient must select either zero- or double-quantum coherence (ZQ or DQ), as shown in the coherence level diagrams. For both ¹H and ¹³C, the coherence pathways selected by the encode and decode gradients are shown as solid lines. The relative signs of the encode and decode gradients depict the coherence selection of the pulse sequences in Fig. 1a, c. The dashed boxes are consistent with those of Fig. 1