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Royal Society of Chemistry, Physical Chemistry Chemical Physics, 8(17), p. 5913-5922, 2015

DOI: 10.1039/c4cp05704j

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Long-lived nuclear spin states far from magnetic equivalence

This paper is available in a repository.
This paper is available in a repository.

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Abstract

Clusters of coupled nuclear spins may form long-lived nuclear spin states, which interact weakly with the environment, compared to ordinary nuclear magnetization. All experimental demonstrations of long-lived states have so far involved spin systems which are close to the condition of magnetic equivalence, in which the network of spin-spin couplings is conserved under pair exchanges of symmetryrelated nuclei. We show that the four-spin system of trans-[2,3-13C2]-but-2-enedioate exhibits a long-lived nuclear spin state, even though this spin system is very far from magnetic equivalence. The 4-spin long-lived state is accessed by slightly asymmetric chemical substitutions of the centrosymmetric molecular core. The long-lived state is a consequence of the locally centrosymmetric molecular geometry for the trans isomer, and is absent for the cis isomer. A general group theoretical description of long-lived states is presented. It is shown that the symmetries of coherent and incoherent interactions are both important for the existence of long-lived states.