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Kumada, Takayuki; Kitagawa, N.; Mori, Shoji; Kumagai, Jun; Aratono, Yasuyuki; Miyazaki, Tsuyoshi

doi:10.1023/a:1021850103903

Cited by 14 publications

(12 citation statements)

References 15 publications

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“…Recently, our group 2 found that the rate constant for the tunneling reaction remarkably increases with the increase in temperature between 5 and 6.5 K, whereas that calculated based on a gas-phase model [3][4][5] has not predicted such an increase. The apparent activation energy for the reaction ͑90 K͒ obtained by fitting the rate constant between 5 and 6.5 K to Arrhenius' equation is very close to that for vacancy formation and migration in solid H 2 (ϳ100 K͒ deduced from temperature dependence of diffusion rate constants of ortho-H 2 ͑o-H 2 ), 6 HD, 7,8 H 2 Ϫ , 9 and charged species. 10 Therefore, it is expected that the tunneling reaction is affected by the vacancy in solid HD.…”

Section: Introductionsupporting

confidence: 61%

Trapping sites of hydrogen atoms in solid HD and D2: An electron spin echo study

Kumada

Noda

Kumagai

et al. 1999

The Journal of Chemical Physics

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Absence of recombination of neighboring H atoms in highly purified solid parahydrogen: Electron spin resonance, electron-nuclear double resonance, and electron spin echo studies Trapping sites of H and D atoms in solid HD and D 2 have been determined using electron spin echo ͑ESE͒ spectroscopy. It was found that all the H and D atoms are trapped in substitutional sites and that the H atoms push back surrounding HD(D 2 ) molecules to produce local lattice distortion around the atoms, whereas the D atoms do not. It is expected that the local lattice distortion is produced by zero-point motion of the H atoms whose amplitude is larger than that of host HD(D 2 ) molecules and that the isotope effect is due to difference in the amplitude between the H and D atoms. The lattice distortion around the H atoms may induce the increase in rate constant for the tunneling reaction DϩDH→D 2 ϩH with the increase in temperature in solid HD reported in Chem.

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Section: Introductionsupporting

confidence: 61%

Trapping sites of hydrogen atoms in solid HD and D2: An electron spin echo study

Kumada

Noda

Kumagai

et al. 1999

The Journal of Chemical Physics

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“…Although the details of the diffusion mechanism of HF cannot be deduced only from the present experimental results, the light mass and the small size of HF are probably essential, which could lower the potential barrier and increase the tunneling frequency to migration. However, Kumada et al 26 reported that the Ne atoms cannot diffuse in solid pH 2 at 4.2 K despite their comparable mass and size with HF. This indicates that there is another driving force that causes the diffusion.…”

Section: Hypothetical Mechanismmentioning

confidence: 99%

Diffusion of hydrogen fluoride in solid parahydrogen

Ooe

Miyamoto

Kuma

et al. 2013

The Journal of Chemical Physics

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We studied diffusion of hydrogen fluoride (HF) in solid parahydrogen (pH2) around 4 K. Diffusion rates were determined from time dependence of FT-IR spectra of HF monomers. The absorption of HF monomers shows temporal decay due to dimerization reaction via diffusion. It was found that the rates are affected by the sample temperature, the initial HF concentration, and annealing of samples. The observed non-Arrhenius-type temperature dependence suggests that the diffusion is dominated by a quantum tunneling process, that is, "quantum diffusion." Deceleration of the diffusion in condensed samples and acceleration in annealed samples were also observed. These results can be attributed to the fact that lower periodicity of samples due to impurities or defects suppresses the quantum tunneling. It seems to be difficult to explain the observed dependences by three possible diffusion mechanisms, exchange of chemical bonds, direct cyclic exchange, and exchange with mobile vacancy. Therefore, we propose a hypothetical mechanism by exchange of vacancies originating from quantum effect.

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“…1 . 29 The decay rate increases with an increase in concentration of HD and n-D 2 in p-H 2 solids. Here, it should be emphasized that the decay rate is proportional to the total concentration of HD, originally contained in p-H 2 samples at natural abundance of 0.03 mol% and artificially added.…”

Section: Structure Of Hmentioning

confidence: 94%

“…where a 4pR eff (D o-H 2 þ D H 6 1)/K op /V o . D oH 2 p exp(À92/T) 48 and D H 6 1 p exp(À93 K/T) 29 above 5 K were reported, whereas K op is independent of T. 48,49 Although R eff should increase with the increase in T asR À1 eff ¼ R N 0 exp(DE o-H 2 -p-H 2 /kT)/r 2 dr on the theory of chemical reaction in liquid phase, 52 the increase is at most B10% of R eff between 4.6 and 6.0 K. Therefore, the variation of EPR intensity in Fig. 8 can be parameterized by a ¼ a 0 exp(À93 K/T) in eqn.…”

Section: (E) Because Electron Spin Relaxation Of Hmentioning

confidence: 99%

“…The quartet lines show a lot of dynamic behaviors such as ortho-para conversion and isotope effects on the formation and decay. [28][29][30] In particular, the isotope effects are remarkable. It has been reported that, as the concentration of HD and D 2 molecules increases, EPR intensity of the quartet lines produced in solid p-H 2 decrease but that of electron bubbles increase.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

H6+ in irradiated solid para-hydrogen and its decay dynamics: Reinvestigation of quartet electron paramagnetic resonance lines assigned to H2?

Kumada

Tachikawa

Takayanagi

2005

Phys. Chem. Chem. Phys.

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The quartet electron paramagnetic resonance (EPR) lines observed in gamma- and X-ray irradiated solid para-H2, which have previously been assigned to H2-, are reinvestigated. We have reassigned the quartet lines to H6 rather than H2- mainly due to comparison of experimentally obtained EPR parameters to theoretical results. Based on the new assignment, trapping site, rotation, ortho-para conversion, quantum diffusion and isotope effect of H+ have been reinterpreted by the precise reanalysis as follows. The H6+ ion is composed of the collinearly aligned H2+ core at the center and two H2 rotors at both ends, occupies a single substitutional site, and has a precession motion around a crystalline axis with the angle of approximately 57 degrees. The ortho-para conversion of H2+ core of H6+ is completed within the time-scale of hours, whereas ortho-H2 molecules near H6+ convert much faster. H6+ diffuses quantum mechanically by the repetition of H6+ + H2 --> H2 + H6+ reaction. The diffusion terminates by the reaction, H6(+) + HD --> H5D(+) + H2, with a HD impurity contained in the para-H2 sample at natural abundance. Finally, we will propose a possible reason why H6+ is produced instead of H3+ in the irradiated solid H2.

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Untitled

Cited by 14 publications

References 15 publications

Trapping sites of hydrogen atoms in solid HD and D2: An electron spin echo study

Trapping sites of hydrogen atoms in solid HD and D2: An electron spin echo study

Diffusion of hydrogen fluoride in solid parahydrogen

H6+ in irradiated solid para-hydrogen and its decay dynamics: Reinvestigation of quartet electron paramagnetic resonance lines assigned to H2?

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