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Effects of coherent many-particle dynamics in providing local site density fluctuations at finite temperatures for hydrogen isotopes in metals are analyzed with tight-binding calculations based on a Hubbard Hamiltonian. These fluctuations increase with temperature, with average deuterium density, and with the magnitude of the site-to-site tunneling. Consequences of such density fluctuations for deuterium dynamics at high concentrations are evaluated within a self-consistent formulation for self-screening of the deuteron-deuteron interaction. This leads to a prediction of significant enhancement of diffusion at high concentration for bosonic species, and anomalous isotope effects for hydrogen diffusion. Extrapolation to the nuclear regime yields estimates of finite-temperature bosonic collective effects on the nuclear reaction rate between deuterons in stoichiometric PdD, yielding rates which are several orders of magnitude below recent experimentally inferred values.

We present fully quantum calculations of the rotational energy levels and spectroscopic rotational constants of the linear OCS molecule in variable size clusters of 4He. The rotational constants of OCS are found to decrease monotonically from the gas phase value as the number of helium atoms increases to N=6, after which the average constant increases to saturation at the large droplet value by N=20. The minimum is shown to indicate a transition from a molecular complex to a quantum solvated molecule, with the former characterized by floppy but near rigid behavior, while the latter is characterized by nonzero permutation exchanges and a smaller extent of rigid coupling.

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