Anwendungen der Kryo-Vakuumtechnik

Haefer, René A.

doi:10.1007/978-3-642-49985-2_10

Cited by 2 publications

(3 citation statements)

References 69 publications

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“…If we suppose that atoms are trapped in two-dimensional imperfections of the crystal lattice, like grain boundaries, then the minimum m of about 460 gives the minimum of the crystallite size of L cr ≈ 60 Å. It is known that the deposition from the gas phase onto a cold substrate at the gas pressure and the substrate temperature far below the triple point parameters gives rise to a polycrystalline film with the crystallite size from tens to hundreds of Å [38]. Based on the data of Ref.…”

Section: Isotope Exchangementioning

confidence: 99%

“…Based on the data of Ref. [38] covering a wide range of the triplet point temperature for various gases, we note that the deuterium crystallite size is expected to be significantly above 60 Å which is characteristic, for example, of CO 2 having much more greater triplet point temperature compared to the deuterium one. Thus, we have to suppose that atoms are trapped by one-dimensional imperfections of the crystal lattice, like dislocations.…”

Section: Isotope Exchangementioning

confidence: 99%

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EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

Dmitriev

2015

J Low Temp Phys

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We present an experimental study of H and D atoms trapped in a solid D 2 matrix. The samples were prepared by quench condensing gaseous nD 2 with small (0.15 %) admixture of molecular nH 2 on a substrate at 1.3-4.2 K. An EPR observation revealed two types of H and D atoms: with narrow-and broad-line spectra. In order to elucidate the origin of the centers we performed an analysis that included comparing the matrix shifts of the hyperfine structure constants, considering the saturation and spin-relaxation times, estimation of the superhyperfine broadening, and evaluation of an effect which the tunneling isotope exchange reaction has on the H and D atoms relative EPR intensities. As a result, the broad-line H and D spectra were attributed to atoms at the substitutional positions in the regular D 2 lattice, while the narrow-line spectra were due to atoms trapped at the one-dimensional structure imperfections (like dislocations). These trapped atoms are capable of moving quickly along the defects with a diffusion coefficient D ≈ 4 × 10 −6 cm 2 /s. The results were compared to earlier observations which allowed us to build a suggestion about the nature of previously found atomic centers in D 2 not explained in the literature.

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Section: Isotope Exchangementioning

confidence: 99%

Section: Isotope Exchangementioning

confidence: 99%

EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

Dmitriev

2015

J Low Temp Phys

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“…condensed Kr film to be almost black body with emissivity ε ≈ 1. The thermal radiation load for the condensation area with ε = 0.9 shielded by an 80 K baffle is 1.85 × 10 −4 W cm −2 [32]. Then, the temperature gradient would be T = 0.003 K for the 1 mm thick film.…”

Section: Sample Preparation and Experimental Set-upmentioning

confidence: 99%

Inertial rotation and matrix interaction effects on the EPR spectra of methyl radicals isolated in ‘inert’ cryogenic matrices

Benetis

Dmitriev

2009

J. Phys.: Condens. Matter

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The CW-EPR lineshapes of methyl and small methyl-like radicals trapped in noble gas matrices at liquid He temperatures are substantially different from the expected classical EPR spectra. At low temperatures they show small or negligible anisotropy in studies using different experimental techniques and have a temperature dependence that differs from systems whose motional dynamics is diffusion controlled. At liquid He temperatures, before the Boltzmann statistics take over in the classical high temperature realm, the spectral intensities are dominated by quantum statistics. These properties, which were obtained experimentally at temperatures about 5 K and lower, and up to about 20 K, can be attributed to quantum effects of inertial rotary motion and its coupling to the nuclear spin of the radical. Methyl-like radicals have nuclear-exchange symmetry and contain the lightest possible isotopes, protons, and deuterons. In the ideal case of absent radical-matrix interaction, the methyl rotation about the central heavier carbon atom guaranties minimal moments of inertia. However, the theoretical interpretation of the above effects and other related quantum effects, as well as recognition of the important physics which lead to them, is not a simple matter. The literature accumulated on the subject over the years is successful but contains several unresolved questions. Recently obtained spectra of methyl radicals in Kr, N(2) and CO matrices, which are less inert than the smaller noble gas Ar, were shown to exhibit greater, but certainly slight, overall anisotropic spectral features while in earlier experimental studies the anisotropy was practically absent. Even gases of smaller radii such as Ne and H(2) at liquid He temperatures show interesting differences as hosts of methyl radicals compared to Ar. Investigation of other possible causes of this difference, not excluding the experimentally controlled ones related to the sample preparation and the MW power saturation of the CW-EPR measurement, were conducted in this work.

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Anwendungen der Kryo-Vakuumtechnik

Cited by 2 publications

References 69 publications

EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

Inertial rotation and matrix interaction effects on the EPR spectra of methyl radicals isolated in ‘inert’ cryogenic matrices

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