Parahydrogen Induced Polarization in Seemingly Symmetric Molecules

L. BULJUBASICH

Simposio; International Symposium on Recent Advances in NMR Applications to Materials; 2010

Since the beginning of the last decade, the technique known as ParaHydrogen Induced Polarization became very popular. Briefly, by cooling hydrogen molecules in the gas phase in the presence of a proper catalyst, a change in the balance of molecules in the para- and ortho-state can be achieved. If the former parahydrogen molecules are transferred to a precursor molecule by a hydrogenation, due to the non-equilibrium nature of the state, the Boltzmann factor does not appear as a limit of the maximum polarization available. Thus, the corresponding polarization can be up to 5 orders of magnitude larger than that obtained in equilibrium NMR. However, the mechanisms for which the hyperpolarization spreads ove the target molecule is a not well explored field. In this contribution, the standard model used to explain the origin of hyperpolarization in PHIP experiments will be revisited, and a more detailed model based on the density operator formalism will be introduced. In addition, two unsolved problems will be presented, with theoretical as well as experimental results.