Electric-field-induced nuclear-spin flips mediated by enhanced sping-orbit coupling

Abstract

Molecules made of identical nuclei of non-zero spin exist in nuclear-spin modifications, and the interconversion of these spin isomers is often forbidden for isolated states 1-3 . The interconversion between the nuclear-spin modifications, however, is promoted by inhomogeneous magnetic fields, such as those present on the surfaces of magnetic materials 4 . Nuclear-spin conversion on diamagnetic and insulating solid substances, on the other hand, is generally considered improbable. Here we present the observation of nuclear-spin flips of H 2 and D 2 occurring on amorphous solid water surfaces with time constants of 370 -140+340 s and 1,220 -580+2,980 s, respectively. To explain these unexpected conversion processes, we propose a model of electric-field-induced nuclear-spin flips. In this model, giant and inhomogeneous electric fields present on the ice surface 5 mix the electronic states of opposite parities by the Stark effect 6 , and significantly enhance the sping-orbit couplings between the electronic singlet-triplet spin states of the molecules. By virtue of these effects, the intramolecular hyperfine contact interaction induces the nuclear-spin conversion. This concept should have implications for controlling nuclear magnetization using external electric fields 7 . © 2011 Macmillan Publishers Limited. All rights reserved.