Low-Frequency Excitation of Singlet-Triplet Transitions. Application to Nuclear Hyperpolarization

Abstract

Coupled pairs of nuclear spins-1/2 support one singlet state and three triplet states. Transitions between the singlet state and one of the triplet states may be driven by an oscillating low-frequency magnetic field, in the presence of couplings to a third nuclear spin, and a weak bias magnetic field. This phenomenon allows the generation of strong nuclear hyperpolarization of 13 C nuclei, starting from the nuclear singlet polarization of a 1 H spin pair, associated with the enriched para spin isomer of hydrogen gas. Hyperpolarization is demonstrated for two molecular systems.