Nuclear spin conversion of methane in pure and rare-gas mixed crystals

Grieger, S.; Friedrich, Hans; Asmussen, B.; Guckelsberger, K.; Nettling, D.; Press, W.; Scherm, R.

doi:10.1007/bf01315649

Cited by 34 publications

(30 citation statements)

References 46 publications

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“…At the same time, there are few reports where the conversion in solid deuterated methane (CD 4 ) was observed [17,18]. In these measurements, the nuclear spin conversion was detected in CD 4 molecules embedded in krypton matrix.…”

Section: Introductionmentioning

confidence: 97%

“…Solid CH 4 undergoes one phase transitions, whereas the deuterated methane exhibits one more transition. The deuterated methane solidifies at equilibrium vapor pressure at 89.78 K and exists in the phase identical to phase I of CH 4 , down to temperature 27.0 K. Similarly as CH 4 , solid deuterated methane exhibits a phase transition to the eight-sublattice partially orientationally ordered state at 27.0 K. Upon further cooling, the crystal undergoes a phase transition, at 22.1 K, to phase III with a complete long-range orientational order.…”

Section: Introductionmentioning

confidence: 99%

“…Methane (CH 4 ) is a hydrocarbon molecule that consists of a single carbon atom (placed at the center) bonded to four hydrogen atoms (at the tetrahedron). This simplest hydrocarbon is a solid at 90.66 K at equilibrium vapor pressure, and displays unchanged crystallographic structure down to 20.4 K. In this structure, called phase I, the tetrahedral molecules are orientationally disordered, performing rotations which do not show any long-range correlation.…”

Section: Introductionmentioning

confidence: 99%

“…Several experiments have shown that this conversion occurs between nuclear spin symmetry species in solid methane (CH 4 ) [4][5][6][7][8][9][10][11][12][13][14][15]. At the same time, there are few reports where the conversion in solid deuterated methane (CD 4 ) was observed [17,18].…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, the results of study of conversion rate in the solid CD 4 and CH 4 at temperatures 2-10 K by using the thermal conductivity technique are presented.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

Pisarska

Stachowiak

Jeżowski

2007

Low Temperature Physics

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show abstract

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…In this paper, the results of study of conversion rate in the solid CD 4 and CH 4 at temperatures 2-10 K by using the thermal conductivity technique are presented.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Pisarska

Stachowiak

Jeżowski

2007

Low Temperature Physics

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Low energy properties of identical and strongly correlated particles

Häusler¹

1996

Annalen der Physik

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Interesting qualitative consequences can arise from the quantum mechanical identity among strongly correlated particles that c w spin. This is demonstrated for properties connected with the low energy excitations in molecular and electronic systems. Spatial permutations among the identical particles are used as the key features.The particular behaviour of rotational tunneling molecules or molecular parts under the influence of dissipation are discussed together with the consequences arising for conversion transitions. The relationship between the thermal shifting of the tunneling line and the conversion rate at low and at elevated temperatures is explicated. The valuable information, that can be extracted from the conversion behaviour after isotopical substitution, is explained in detail. At low temperatures qualitative changes are predicted for the conversion rate by deuteration. Weakly hindered rotors show, also experimentally, drastic isotopic effects.The second part is devoted to finite systems of strongly interacting electrons that appear in semiconductor nano-structures. The lowest excitation energies are strongly influenced by the interaction. They can be understood and determined starting from the limit of crystallized electrons by introducing localized many particle 'pocket states'. The energy levels show multiplet structure, in agreement with numerical results. The total electron spin, associated with the low energy excitations, is crucially important for the nonlinear transport properties through quantum dots. It allows for instance to explain the appearance of negative differential conductances.

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Phonon scattering by quantum rotor and spin conversion in solid Kr‐CH ₄ solutions

Кривчиков¹,

Gorodilov

Korolyuk

et al. 2004

phys. stat. sol. (c)

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The measurement results on the thermal conductivity K(T) of solid Kr 1-x (CH 4 ) x solutions in the interval 2-40 K, x = 0-1, are reported. The temperature dependences K(T) taken in the solutions in concentrated orientationally-ordered and orientationally-disordered phases have features that are not typical of dielectric crystals. It is shown that the anomalous K(T) is caused by strong single-phonon resonance scattering at a weakly hindered quantum rotor-the CH 4 molecule with the nuclear spin I = 1.1 Introduction. A molecule freely rotating in a crystal does not interact with its surroundings. In actual practice, however, when certain properties of condensed phases containing rotating molecules (rotors) are considered, it is important to take into account even weak noncentral interactions of these molecules with the surrounding particles. The rotor-lattice interaction in a crystalline system is called a phonon-rotation interaction (PRI) [1]. Precisely PRI brings the translational vibrations of the lattice and the rotation of the molecules to equilibrium. PRI can in particular affect the thermal conductivity of the substance [2][3][4]. In the crystalline state the character of molecular rotation is dependent not only on the force of interparticle interactions but on the thermal vibrations of the lattice as well.In the solid Kr 1-x (CH 4 ) x solution we can observe quantum-mechanical rotation at low temperatures and rotational diffusion of the molecules at high temperatures. Owing to the spherical symmetry of Kr atoms and the close Lennard-Jones potential of methane and krypton, the rotation of CH 4 molecules is weakly hindered, no considerable stress are induced in the lattice of solid solution and its components are characterized by high mutual solubility in the solid phase.This investigation of thermal conductivity was made on a two-component crystal system of weakly hindered rotors and inert gas atoms whose parameters of the Lennard-Jones potential were close to those of the rotors.The goal of this work was to investigate the influence of PRI on the thermal conductivity of solid CH 4 -Kr solutions in which the CH 4 subsystem is viewed as an ensemble of rotors interacting with one to another and with the translational vibrations of the lattice. Varying the CH 4 concentration in the solution, it is possible to trace how the PRI changes on transition from the system with a weak noncentral interaction to the system with a party orientational order in orientationally-ordered phase II of methane. Three fourths of the CH 4 molecules perform heavily hindered rotational motion (small-angle orientational vibrations-librations) in a strong anisotropic molecular field of D 2d symmetry; one fourth of the molecules (rotors) rotate almost freely in the crystal field having the octahedral symmetry O h . Each of these types of rotational excitations scatters the phonons and contributes to the thermal resistance. It is found [5],

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Nuclear spin conversion of methane in pure and rare-gas mixed crystals

Cited by 34 publications

References 46 publications

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

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

Low energy properties of identical and strongly correlated particles

Phonon scattering by quantum rotor and spin conversion in solid Kr‐CH ₄ solutions

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Nuclear spin conversion of methane in pure and rare-gas mixed crystals

Cited by 34 publications

References 46 publications

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

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

Low energy properties of identical and strongly correlated particles

Phonon scattering by quantum rotor and spin conversion in solid Kr‐CH 4 solutions

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Phonon scattering by quantum rotor and spin conversion in solid Kr‐CH ₄ solutions