CO/pH2: A Molecular Thermometer |
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Authors: | Simon Tam Mario E Fajardo |
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Affiliation: | (1) Propulsion Directorate, US Air Force Research Laboratory, AFRL/PRSP, Bldg. 8451, Edwards AFB, CA 93524-7680, USA |
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Abstract: | We utilize reversible temperature dependent changes in the IR absorption spectrum of CO molecules isolated in solid parahydrogen (pH2) to probe bulk temperature changes during rapid vapor deposition. The intensity of a well resolved feature near 2135 cm–1 increases monotonically with temperature over the 2 to 5 K range. The thermally populated initial state of this transition lies 12 K above the CO/pH2 ground state. During the deposition of 100 ppm CO/pH2 samples, we detect temperature gradients 10 K/cm in 0.1 cm-thick samples subjected to heat loads 10 mW/cm2. The resulting estimated thermal conductivity (TC) is 3(±2) mW/cm-K, averaged over the 2 to 5 K region. This value is 1000 times lower than the TC of single crystal solid pH2, and 10 times lower than previously measured for pH2 solids doped with 100 ppm concentrations of heavy impurities Manzhelii, Gorodilov, and Krivchikov, Low Temp. Phys. 22, 131 (1996)]. We attribute this abnormally low TC to the known mixed fcc/hcp structure of the rapid vapor deposited solids. |
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