| 概 要 |
Singlet nuclear spin states are quantum states of a nuclear spin-1/2 pair that are antisymmetric with respect to spin exchange, and which have total spin zero. They are therefore non-magnetic and protected against many important relaxation mechanisms. These states often exhibit long relaxation times which may exceed the normal relaxation time T1 by an order of magnitude or even more. In the special case of the 15N spin pair in 15N-labelled nitrous oxide, the nuclear singlet lifetime can be as long as 25 minutes.
I will discuss the phenomenon of singlet nuclear spin order in a variety of contexts - including gas-phase parahydrogen, small molecules in solution, and also some examples of nuclear singlet states in solids. I will discuss how nuclear singlet spin order may be generated from magnetization, how it is maintained, and how it is converted back into observable magnetization.
Our latest work in the field includes the generation of hyperpolarized nuclear singlet order using dynamic nuclear polarization. We have been particularly interested in the properties of nearly equivalent spin pairs, where the hyperpolarized singlet order is long-lived in high magnetic field, even without any external intervention. We have designed and demonstrated molecular systems that exhibit 13C singlet lifetimes of more than 10 minutes. Together with many collaborators, we have also studied the nuclear singlet states of parawater molecules trapped inside fullerene cavities, using neutron scattering and infrared spectroscopy, as well as NMR.
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