Overview Over DNP Mechanisms

Dynamic nuclear polarization describes a process whereby spin polarization is transferred from unpaired electrons to nuclear spins. This process exploits the much larger polarizations arising from electrons, which can be close to 100% at 

The overall Hamiltonian of an electron-nuclear spin system in a magnetic field is given by  

The first two terms describe the electron and nuclear Zeeman interactions, respectively, with cOe = and cOn = where ye and y- are the gyromagnetic ratios of electrons and nuclei, respectively, and Bq represents the external magnetic field strength. S and I are used for electron and nuclear spin operators, respectively. For indices, this review always uses n for nucleus and e for electrons, i.e., yj = yg and yi = y . 

Abragam and Goldman recognized that the dipolar interaction causing relaxation between nuclei determines the polarization time in the solid state. Nuclear relaxation is also relevant in solution, as will be shown in 2.1. Moreover, recent work by Vega has paid attention to nuclear spin diffusion associated with DNP, the key mechanism for transfering magnetization from molecules in contact with the radical to other nuclei in the solid state [43]. 

In solution, the term that seems most important for DNP is //gn, describing the electron-nuclear interactions, which are governed by the dipolar interaction hP and the scalar Eermi contact interaction where  

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