Changes in the structure of amorphous solid water films, grown by vapour deposition on a copper substrate at 75 K and then held at 120 K for 10 min to effect pore collapse, have been observed in the ranges 122-139 K and 150-162 K using positronium annihilation spectroscopy. It is proposed that the former is associated with the glass transition, with an effective activation energy of 0.266(3) eV. The data for the latter, which exhibit minima suggesting the temporary introduction of molecular disorder, can be processed to yield an effective activation energy of 0.47(2) eV, and are consistent with either a structural reorganization of the crystalline lattice or a relaxation of the amorphous structure mediated by defect migration.
PACS. 05.20. -Statistical mechanics. PACS. 52.25P. -Emission, absorption, and scattering of radiation.Abstract. -The effective potential between ions screened by weakly degenerate electrons in a dense hydrogen plasma is derived by a systematic procedure and applied to the calculation of the second moment of the electric-microfield distribution function.
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