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The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of the Kr[sub 1-c](CH[sub 4])[sub c] solid solutions at c=0.05–0.75 in the temperature region 2–40 K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons on CH[sub 4] molecules with the nuclear spin I=1 (the nuclear spin of the T species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity κ(T) leads to a well-defined minimum on κ(T). The temperature of the minimum depends on the CH[sub 4] concentration. It was shown that the nonmonotonic increase of the anisotropic molecular field with the CH[sub 4] concentration is caused by a compensation effect due to corrections in the mutual orientations of the neighboring rotors at c κ>0.5. The temperature dependence or Kr[sub 1-c](CH[sub 4])[sub c] is described within the Debye model of thermal conductivity taking into account the lower limit of the phonon mean free path. It is shown that phonon–rotation coupling is responsible for the anomalous temperature dependence of the thermal resistance at varying temperature. It increases strongly when the quantum character of the CH[sub 4] rotation at low temperatures changes to a classical one at high temperatures. A thermal conductivity jump (a sharp increase in κ(T) within a narrow temperature range) was also observed. The temperature position of the jump varies from 9.7 to 8.4 K when the CH[sub 4] concentration changes from 0.25 to 0.45. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the influence of an orthodeuterium impurity on the thermal conductivity of solid parahydrogen. Thermal conductivity of parahydrogen samples at deuterium concentration; Relative change of the force constants and radial distortion; Deviations from classical scattering of phonons by an isotopic impurity.

The thermal conductivity of a solid parahydrogen crystal with methane admixtures was measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixtures at 13 K. The concentration of CH[sub 4] admixture molecules in the gas varied from 5 to 570 ppm. A very broad thermal conductivity peak with an absolute value of about 110 W/(m·K) was observed at 2.6 K. The data were interpreted using Callaway’s model with resonance scattering of phonons by quasilocal vibrations of CH[sub 4] molecules and phonon–grain boundary and phonon–phonon scattering. As grain boundary scattering increases, the broadening of the peak decreases. The analysis shows that a solid mixture of p-H[sub 2] and CH[sub 4] is a heterogeneous solution for CH[sub 4] concentration higher than 0.1 ppm. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The thermal conductivity of CH[sub 4]-Kr solid solutions is investigated at CH[sub 4] concentrations 0.2-5.0% in the temperature range 1.8-40 K. It is found that the temperature dependence of the thermal conductivity has features typical of resonance phonon scattering. The analysis of the experimental results shows that the main contribution to the impurity-caused scattering of phonons is made by the scattering on rotational excitations of the nuclear spin T-species of CH[sub 4] molecules. The phonon-rotation interaction parameter is estimated. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The thermal conductivity of orthodeuterium crystals containing a neon impurity is investigated in the temperature interval 1.8-17 K. The results of the measurements are described in the framework of the relaxation-time model with allowance for phonon-phonon scattering processes. The intensity of the normal scattering processes for deuterium are determined. The existing theoretical models are used to estimate the intensity of the phonon scattering processes for a number of cryocrystals. The calculated intensity of the normal processes is compared to the experimental result. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]