Observation of relaxation of molecular spins in CH4 and CD4 crystals in thermal conductivity experiment

Pisarska, E.; Stachowiak, P.; Jeżowski, A.

doi:10.1063/1.2755190

Cited by 7 publications

(2 citation statements)

References 19 publications

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“…There have been numerous studies of the NSC in CH 4 in noble gas matrices and in para-hydrogen matrices (see refs , and references cited therein). Several techniques were used to measure the NSC in solid CH 4 : nuclear magnetic resonance (NMR), thermal conductivity, neutron scattering, and infrared spectroscopy. ,, The requirement on the symmetry of the wave function pins rotational levels to nuclear spins. This makes infrared spectroscopy a good tool to probe the spin populations of each isomer via measurements of rovibrational transitions.…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases

Emtiaz

Toriello

et al. 2019

J. Phys. Chem. A

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Infrared spectroscopy was employed to study thin films of solid methane at low temperatures. We report new measurements of temporal changes of infrared spectra of methane ice in the ν3 and ν4 bands due to nuclear spin conversion upon rapid cooling from 30 to 6.0–11.0 K. The relaxation rates of the nuclear spin were found to be a function of temperature. The activation energy associated with the relaxation has been determined over an extended temperature range. We also found a new metastable phase of methane ice upon deposition at T < 7 K. After the deposition at 6 K and annealed to a higher temperature, a phase transition from the metastable phase to a stable crystalline phase takes place. We found that the relaxation has different activation energies below and above 8.5 K. From a quantitative analysis of the ν3 and ν4 IR bands, we suggest that the metastable phase is a crystalline phase with a degree of orientational disorder between the two known stable solid phases.

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Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases

Emtiaz

Toriello

et al. 2019

J. Phys. Chem. A

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“…In the region with phase III inclusions, the thermal conductivity k( ) T is influenced by the temperature prehistory of the sample. The nuclear spin conversion of CH 4 molecules causing relaxation of k( ) T [21,22] has little effect on k( ) T . In terms of quality, the change of the thermal conductivity versus sample composition follows general expectations: the thermal conductivity of the solutions is lower than that of pure crystals.…”

Section: Resultsmentioning

confidence: 99%

Orientational isotopic effects in the thermal conductivity of CH4∕CD4 solid solutions

Кривчиков

Stachowiak

Pisarska

et al. 2007

Low Temperature Physics

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The thermal conductivity of (CH 4 ) 1-c (CD 4 ) c solid solutions with c = 0, 0.03, 0.065, 0.13, 0.22, 0.4, 0.78, and 1.0 has been measured in the region of existence of three orientational phases: disordered (phase I), partially ordered (phase II) and completely ordered (phase III). The temperature range is 1.3-30 K. It is shown that the thermal conductivity has different temperature dependences k( ) T in these phases. Its value increases with the degree of the orientational order in the phase. In phase I the thermal conductivity is independent of c and weakly dependent on T. The impurity effect in k( ) T is much stronger in the low-temperature part of phase II than in phase III. As the concentration c grows, the k( ) T curve of phase II approaches the dependence k( ) T typical of phase I. There is a hysteresis in the vicinity of the II«III phase transition. In phase III the impurity effect in k( ) T can be considered as phonon scattering at rotational defects developing due to the difference between the moments of inertia of the CH 4 and CD 4 molecules. The obtained dependences of thermal conductivity on temperature and concentration can be explained qualitatively assuming that the dominant mechanism of phonon scattering is connected with the interaction of phonons with the rotational motion of the molecules in all of the three orientational phases of the CH 4 -CD 4 system. PACS: 63.20.-e Phonons in crystal lattices; 66.70.+f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves.

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Infrared spectroscopic investigation of nuclear spin conversion in solid CH4

Sugimoto

Yamakawa

Arakawa

2015

The Journal of Chemical Physics

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Infrared spectra of solid CH4 were studied in the ν3 and ν4 vibrational regions. The phase I crystal around 30 K showed broad absorption bands, whereas the phase II crystal at 6.9-10.3 K exhibited splitting of these bands after annealing above 20 K. The split peaks were assigned to the librating and almost freely rotating molecules in phase II on the basis of the peak spacings and time evolution of the peak intensities. From the quantitative analysis of the temporal changes of the R(0) and R(1) peak intensities, the relaxation rates of the numbers of molecules with J = 0 (I = 2) and J = 1 (I = 1) were determined in the temperature range of 6.9-10.3 K. We fitted the function resulting from a combination of direct and indirect relaxation processes mediated by phonons to the temperature dependence of these rates and obtained the activation energies of the indirect process: C ≃ 36 K. Since this value is higher than the energies of perturbed J = 2 states relative to the J = 1 state, we argue that the nuclear spin conversion through the J = 3 state also takes place.

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Observation of relaxation of molecular spins in CH4 and CD4 crystals in thermal conductivity experiment

Cited by 7 publications

References 19 publications

Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases

Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases

Orientational isotopic effects in the thermal conductivity of CH4∕CD4 solid solutions

Infrared spectroscopic investigation of nuclear spin conversion in solid CH4

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