Figure 2.

(a)–(b) Visualization of the PAIN-CP spin dynamics subspace. The space can be seen as a coupled basis between a ZQ/DQ fictitious spin I (involving the nitrogen spin N and the carbon spin C) and a proton spin H (assisting spin). The red arrows indicate the transverse PAIN-CP recoupling axis and the longitudinal off resonance contribution (from autocross terms, see Sec. 2C) which result in a tilting of the effective recoupling axis. [see SI Sec. 1 for fictitious ZQ/DQ spin operator notations] (Ref. ²⁶).