Orientational ordering in quench-condensed H[sub 2] measured by AC calorimetry

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Journal of Low Temperature Physics; (United States)

DOI:https://doi.org/10.1007/BF00681874· OSTI ID:5829720

Phelps, R B; Birmingham, J T; Richards, P L ^[1]

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1. Univ. of California, Berkeley, CA (United States) Lawrence Berkeley Laboratory, CA (United States)

The heat capacity of quench-condensed normal- and para-hydrogen has been measured using ac calorimetry. The measurements were made at temperatures from 1.6 to 3.7 K on sapphire and evaporated gold substrates. The range of exposures studied was 0.24 to 3.3 [angstrom][sup [minus]2], yielding estimated coverages from 0.07 to 2.5 [angstrom][sup [minus]2]. For reference, monolayer completion of H[sub 2] on graphite occurs at a coverage of 0.1 [angstrom][sup [minus]2]. For normal-hydrogen (n-H[sub 2]) on a few of the sapphire substrates, the heat capacity as a function of temperature exhibits a peak at 1.8 K, followed by a rapid decrease. For the n-H[sub 2] data on all other substrates, a negative slope is observed at the lowest temperatures measured, which is consistent with a peak below the studied temperature range. The authors attribute these effects to a bulk-like orientational ordering transition. The coverage dependence of the peak is not consistent with the predictions of a model of finite-size effects. They conclude that the dominant broadening of the peak is inhomogeneous. The desorption rate is deduced from the time dependence of the heat capacity and is found to agree with previously published values. The ortho-to-para conversion rate is comparable to that of bulk hydrogen.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5829720
• Journal Information: Journal of Low Temperature Physics; (United States), Journal Name: Journal of Low Temperature Physics; (United States) Vol. 92:1-2; ISSN JLTPAC; ISSN 0022-2291
• Country of Publication: United States
• Language: English

Related Subjects

665430* -- Other Topics in Quantum Fluids & Solids-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CALORIMETRY
CORUNDUM
DESORPTION
ELEMENTS
FILMS
GOLD
HYDROGEN
METALS
MINERALS
NONMETALS
ORDER-DISORDER TRANSFORMATIONS
OXIDE MINERALS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SAPPHIRE
SORPTION
SPECIFIC HEAT
SUBSTRATES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0000-0013 K
THERMODYNAMIC PROPERTIES
THIN FILMS
TRANSITION ELEMENTS