Erika G. Kisvarsanyi

QUANTUM TUNNELING IN SOLID D2 AND SOLID H2

We report calculations of quantum tunneling in solid deuterium and solid hydrogen using a most-probable-escape-path method for tunneling in quantum crystals. We estimate the rates for tunneling by quantum-mechanical exchange in solid H[sub 2] and D[sub 2] and calculate specifically the tunneling of HD impurities and paradeuterium impurities in solid parahydrogen and solid orthodeuterium. These calculations are compared with the results of recent experiments.

The quantum diffusion of isotopic impurities in solid hydrogen

Abstract The diffusion of HD molecules, present as isotropic impurities in solid hydrogen, is calculated in the temperature range where the quantum tunneling of the impurities is hindered by scattering from vacancies. The vacancy-impurity scattering cross section is calculated using a classical approximation. The results are compared with recent NMR measurements of the impurity diffusion at low temperatures.

Theory of NMR multiple echoes in solid hydrogen

We have examined the theory of NMR multiple echoes developed for solid3He to determine whether multiple echoes could be observed in solid hydrogen. We were particularly interested in the possibility of testing for low frequency quantum tunneling motions in solid hydrogen by the observation of multiple echoes. We find that for easily accessible nuclear spin polarizations, P > 12%, multiple echoes would be observed for HD impurities in solid parahydrogen if motional narrowing is effective in increasing the HD nuclear spin-spin relaxation time T2 to the order of 1 msec. These values for T2, which have been observed for HD impurity concentrations of the order of 1%, are larger than the calculated rigid lattice values and can be attributed to quantum tunneling at frequencies of the order of 1kHz.

Quantum diffusion of isotopic impurities in solid4He and solid H2.

Abstract The temperature dependence of the diffusion of3He impurities in solid4He and HD impurities in solid para-H2 is calculated for the regime where coherent motion of the isotopic impurities is interrupted by scattering from vacancies or phonons. In both cases the best fit to the experimental data is obtained using a model including vacancy scattering rather than phonon scattering.

Nuclear spin-lattice relaxation of isotopic impurities in solid hydrogen

We report calculations of the nuclear spin-lattice relaxation of isotopic impurities (HD) in solid hydrogen. The temperature-independent relaxation observed at low temperatures is attributed to the quantum tunneling of the impurities, and the pronounced minimum observed at intermediate temperatures is associated with scattering from thermally excited vacancies.