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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Clustering and Heterogeneous P1 Distributions in Diamond Govern DNP Mechanisms at 6.9 and 13.8 T
Orit Nir-Arad1, David H Shlomi1, Raj K Chaklashiya2,3
1School of Chemistry, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 6997801, Israel.
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Nitrogen substitutions (P1 centers) in diamonds were shown to provide significant 13C hyperpolarization at room temperature and high fields, with the presence of P1 clusters hypothesized to be essential. We compare the 6.9 and 13.8 T 13C dynamic nuclear polarization (DNP) and electron paramagnetic resonance spectra of two single-crystal diamonds: one with a high P1 concentration (∼20 ppm) and abundant P1 clusters, and another with a low P1 concentration (∼3.5 ppm) and no clusters. The first exhibits a 540 ± 180 nm 13C NMR enhancement with broad and narrow DNP features, whereas the second displays only weak, sharp DNP peaks after prolonged irradiation. The dependence of 13C polarization buildup rate on millimeter-wave frequency distinguishes solid-effect (SE) from cross-effect (CE), confirming P1 clusters are essential for efficient high-field DNP. Moreover, we show that in the high-P1-concentration diamond, the SE and CE polarize distinct pools of 13C nuclei, demonstrating DNP's ability to map the spatial distribution of diamond defects.
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