title: Long-lived nuclear spin states far from magnetic equivalence.
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 all pair exchanges of symmetry-related nuclei. We show that the four-spin system of trans-[2,3-(13)C2]-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.
authors: School of Chemistry, University of Southampton, University Road, Southampton, UK. mhl@soton.ac.uk.
authors: Gabriele
authors: G
authors: Stevanato
authors: Soumya Singha
authors: SS
authors: Roy
authors: Joe
authors: J
authors: Hill-Cousins
authors: Ilya
authors: I
authors: Kuprov
authors: Lynda J
authors: LJ
authors: Brown
authors: Richard C D
authors: RC
authors: Brown
authors: Giuseppe
authors: G
authors: Pileio
authors: Malcolm H
authors: MH
authors: Levitt