<i>T</i> 1– <i>T</i> 2 microscale correlation relaxometry for <i>in situ</i> high-pressure nuclear magnetic resonance

Over the last decade, frequency-domain in situ high-pressure nuclear magnetic resonance (NMR) spectroscopy in diamond anvil cells (DACs) has been employed as a structural and electronic probe of condensed matter systems at pressures well into the megabar range. However, extensive spin interactions and sample heterogeneities under pressure often lead to significant spectral overlap, inhibiting independent observation of chemically similar spin subspecies in the same sample. In this work, we introduce a time-domain relaxometry framework specifically suited for DAC experiments. Experimental flexibility and operational robustness are benchmarked on three hydrogen-rich molecular solids at pressures up to 72 GPa. We demonstrate that T1–T2 relaxometry can separate distinct proton populations in relaxation space even when the corresponding frequency-domain spectra are strongly broadened and overlapping, thereby establishing a practical route to relaxation-based high-pressure NMR analysis in molecular solids.