Single-quantum ST coherences can be converted fully to double-quantum ST (DQST) coherences with a CT selective -pulse . Fig. also shows a DQST HETCOR spectrum (red traces) by adding two -pulses in the pulse sequence (Fig. ). The second order quadrupolar broadening to the DQSTs is 1/9 in frequency or 1/18 in ppm to that of CT. The 35 Cl dimension is nearly isotropic; made possible with double-CP to the STs. It is worth noting that TRAPDOR recoupling can also generate correlation with all transitions including the DQSTs of a spin S = 3/2 simultaneously using the T-HMQC experiment . Fig. shows that near isotropic resolution can be obtained with both methods. In the present instance, the proton T2 relaxation does not contribute to the 35 Cl linewidth as opposed to the case of T-HMQC. Spindiffusion among protons can occur during the 1 H spinlock even under fast MAS causing relayed peaks in the DCP HETCOR spectra. 35 Cl CT (black), ST (blue), or DQST (blue) coherences. For the ST and DQST spectra, the transmitter offset was set +180 kHz from CT near the second ST spinning sideband throughout, except for the CT-selective π-pulses. Each 2D experiment was acquired with indirect spectral widths of 22.5 kHz, 64 complex t1 points, 16 transients per t1 point, and a recycle delay of 10 s. Other experimental parameters are described in Fig. .