V. V. Dudkin

Thermal conductivity of solid krypton with methane admixture

The thermal conductivity of CH4–Kr solid solutions is investigated at CH4 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 CH4 molecules. The phonon–rotation interaction parameter is estimated.

Anisotropy of the Thermal Conductivity of Parahydrogen Crystals

The anisotropy of thermal conductivity of parahydrogen crystals has been observed for the first time. The thermal conductivity measurements have been made on samples of different diameters at the temperature range from 2 to 8 K.

Detection of nuclear spin conversion of CD4 molecules in a solid solution of deuteromethane in krypton

The heat capacity of the solid solutions (CD4)0.05Kr0.95 and (CD4)0.05Kr0.948(O2)0.002 are investigated in the temperature interval 0.7–1.6 K. The contribution to the heat capacity of the solutions from the rotational subsystem is separated out. Conversion between the A and T nuclear spin species of CD4 is detected. It is shown that in unconcentrated solutions of methane isotopes in krypton the rate of conversion is larger for the deuteromethane molecules than for the methane molecules.

Heat capacity of solid solutions of deuteromethane in krypton. Nuclear spin conversion in CD4 molecules

A study is made of the heat capacity of the binary solid solutions (CD4)0.01Kr0.99 (in the temperature interval ΔT=0.9–7 K) and (CD4)0.05Kr0.95 (ΔT=0.7–20 K) and of the ternary solid solutions (CD4)0.01Kr0.988(O2)0.002 (ΔT=0.7–11 K) and (CD4)0.05Kr0.948(O2)0.002 (ΔT=0.8–4 K). The contribution of the rotational subsystem to the heat capacity of the solutions is separated out. The influence of temperature, oxygen impurities, and the interaction between the deuteromethane molecules on the effective conversion rate is studied. The energy differences between the lowest-lying levels of the nuclear spin species A and T of deuteromethane is determined, and the effective characteristic conversion times are found. Rapid conversion of isolated CD4 molecules is observed in CD4–Kr solutions. It is shown that in the CD4–Kr solutions, as in CH4–Kr solutions, a hybrid mechanism of conversion is dominant at low temperatures (T<1.4 K), and the “bottleneck” governing the conversion rate is the intermolecular effective octup...

The role of normal processes in the thermal conductivity of solid deuterium

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.

Isotopic effects in the heat capacity of concentrated orientationally disordered solid solutions of methane and deuteromethane in krypton

The heat capacity of orientationally disordered solid solutions (CH4)nKr1−n (n=75 and 78 mole% CH4 in the temperature interval ΔT=0.8–20 K) and (CD4)nKr1−n (n=50, 60, and 70 mole% CD4, ΔT=0.6–30 K) is investigated. At liquid-helium temperatures the temperature dependences of the molar heat capacities of the rotational subsystems of the solutions are qualitatively and quantitatively very different. One of the main reasons for the effect is that in the concentrated solutions investigated the CD4 molecules are in a substantially stronger molecular field than the CH4 molecules. This is because in low-energy states the effective octupole electric moment of CD4 molecules, which determines the molecular field, is larger than the effective octupole moment of the more quantum molecules CH4. The weak concentration dependences of the heat capacity of the solutions studied are due to the influence of frustration, which weakens the molecular fields produced at the lattice sites by the surrounding molecules. No evidenc...

Phase transitions in Kr–CH4 solid solutions and rotational excitations in phase II

The heat capacity CP of Kr-nCH4 solid solutions with CH4 concentrations n=0.82, 0.86, and 0.90 and of solutions with n=0.90, 0.95 doped with 0.002 O2 impurity is investigated under equilibrium vapor pressure over the interval 1–24K. The (T,n) phase diagram of Kr-nCH4 solid solutions is refined, and the region of two-phase states is determined. The contribution of the rotational subsystem, Crot, to the heat capacity of the solutions is separated. Analysis of Crot(T) at T<3K makes it possible to estimate the effective conversion times τ and the energy gaps E1 and E2 between the tunneling levels of the A,T and A,E nuclear-spin species of CH4 molecules in the orientationally ordered subsystem and to determine the effective energy gaps E1 between the lowest levels of the A and T species. The relations τ(n) and E1(n) stem from changes of the effective potential field in result of the replacement of CH4 molecules by Kr atoms at sites of the ordered sublattices. The effective gaps EL between a group of tunneling ...

Quantum effects in the thermal conductivity of solid krypton–methane solutions

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of the Kr1−c(CH4)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 CH4 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 CH4 concentration. It was shown that the nonmonotonic increase of the anisotropic molecular field with the CH4 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 Kr1−c(CH4)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 ...

Low Temperature Anomaly of Heat Capacity of CD4 Rotors in Solid CD4–Kr Solution

Heat capacity of the solid Kr–CD4 (13% CD4) solution has been investigated. It is shown that the temperature dependence of the heat capacity Crot of the rotational subsystem in this solution is radically different from the corresponding dependences in the previously studied Kr–CD4 (1%, 5% CD4) and Kr–CH4 (5–60%) solutions. A model is proposed to explain the observed dependence Crot (T). The experimental results can be described taking into account the contribution to the heat capacity from CD4 molecules that are in weak, medium and strong molecular fields. The mean concentrations and energy differences between the ground and first excited energy levels of the CD4 molecules in these molecular fields have been estimated.