Dynamic Tunneling Polarization as a Quantum Rotor Analogue of Dynamic Nuclear Polarization and the NMR Solid Effect

Abstract

The populations of the tunneling states of CH(3) are manipulated by rf irradiation of weakly allowed sideband transitions within the manifold of tunneling-magnetic levels. Substantial positive and negative CH(3) tunneling polarizations are observed, providing a quantum rotor analogue of dynamic nuclear polarization and the solid effect in NMR. The field-cycling NMR technique used in the experiments employs level crossings between tunneling and Zeeman systems to report on the tunneling polarization. The tunneling lifetimes are measured and the field dependence investigated.

Quantum rotation and translation of hydrogen molecules encapsulated inside C 60 : temperature dependence of inelastic neutron scattering spectra

“…Hence, the exchange splitting can be much smaller than the rotational constant, but invariably larger than the 1 H Zeeman splitting. Then, magnetic dipole-dipole interactions (nuclear-nuclear or electron-nuclear) may have sufficient magnitude relative to hν t to mediate space-spin transitions with significant probability and hence make them accessible to NMR spectroscopy [17][18][19][20]. Likewise, hindered rotation of dihydrogen has been shown to give rise to tunnelling splittings that reveal themselves in NMR spectra when coherent tunnelling and an associated exchange interaction are present [21].…”

Transfer of the Haupt-hyperpolarization to neighbor spins

“…The phenomenon is related to the Haupt effect which was discovered in 1972 [2] and has since then very often been debated in the literature [3][4][5][6][7][8][9][10][11][12][13]. An obvious question after the observation of the Haupt effect in high resolution was, whether the hyperpolarization observed can be transferred from the methyl groups towards neighbor spins.…”

Spin-symmetry conversion in methyl rotors induced by tunnel resonance at low temperature

“…Direct measurements of the tunneling lifetime have been recently measured for CH 3 groups with tunnel frequencies of order 500 kHz using the dynamic tunneling polarization effect in NMR. 25 In that study, lifetimes were typically of order T 1 suggesting 1 H-1 H dipolar interactions mediate the thermal equilibration of the tunnel reservoir. In phenylacetone the tunnel frequency is significantly larger than the dipolar frequencies therefore, at fields outside the level crossing regions, it is probable the tunneling lifetime is longer compared with T 1 given the likely magnitude of the spectral density available to drive A-E transitions.…”