Actions for AC microcalorimetry of adsorbates on evaporated metal films [electronic resource] : Orientational ordering of H{sub 2} multilayers

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AC microcalorimetry of adsorbates on evaporated metal films [electronic resource] : Orientational ordering of H{sub 2} multilayers

Published
Washington, D.C. : United States. Dept. of Energy, 1991.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
110 pages : digital, PDF file
Additional Creators
Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
We have improved and extended a novel ac calorimetric technique for measuring the heat capacity of adsorbates on evaporated metal films. Metallic substrates are of particular interest in current studies of the thermodynamics of adsorbed molecules. The method described in the present work is only calorimetric technique which allows measurements of molecules on simple metallic surfaces. Among other improvements, we have achieved significant progress in the preparation and characterization of the evaporated metal film. We have applied this novel technique to a study of hydrogen multilayers on gold and sapphire substrates. We have shown that samples of normal-hydrogen with a nominal coverage n of approximately 25 monolayers (ML) undergo a bulk-like orientational ordering transition. The transition is suppressed as the coverage is decreased, and no sign of the transition remains above 1.6 K for n ≈ 1 ML. For n ≲ 8 ML, the peak in the heat capacity exhibits signs of finite-size effects. At higher coverages, finite-size effects are not observed, and the shape of the peak depends strongly on the substrate. We conclude that the peak is inhomogeneously broadened for n ≲ 8 ML. This work represents the first measurements of the heat capacity due to orientational ordering in adsorbed hydrogen. The results of an earlier experiment involving vibrational spectroscopy of adsorbed molecules are included in the Appendix. In this work, we have used infrared emission spectroscopy to study the spectral region in the vicinity of the C=O stretch vibration of bridge-bonded CO on Pt(111).
Report Numbers
E 1.99:lbl--31576
lbl--31576
Subject(s)
Other Subject(s)
Dissertation Note
Thesis (Ph.D.); PBD: Nov 1991
Note
Published through SciTech Connect.
11/01/1991.
"lbl--31576"
"DE92008317"
Phelps, R.B.
Funding Information
AC03-76SF00098
View MARC record | catkey: 14456797