Time evolution of the rate constant for the tunneling reaction H2 + D → H + HD in solid D2H2 mixtures at very low temperature

Kumada, Takayuki; Aratono, Yasuyuki; Miyazaki, Tsuyoshi

doi:10.1016/s0301-0104(96)00188-7

Cited by 4 publications

(3 citation statements)

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“…The D atoms cannot move via exchange tunneling because the D atom gets trapped in an HD molecule after the first D + H 2 → HD + H exchange reaction. This isotopic variant of the H atom exchange reaction is exothermic (−260 cm –1 ) due to the lower zero-point vibrational energy of HD compared to H 2 and readily occurs with a time constant of 77 s at 4.2 K in solid D 2 -H 2 mixtures . Accordingly, the growth in the HCO peak after photolysis can be explained by the H + CO → HCO reaction.…”

Section: Experimental and Resultsmentioning

confidence: 99%

“…This isotopic variant of the H atom exchange reaction is exothermic (−260 cm −1 ) due to the lower zero-point vibrational energy of HD compared to H 2 and readily occurs with a time constant of 77 s at 4.2 K in solid D 2 -H 2 mixtures. 9 Accordingly, the growth in the HCO peak after photolysis can be explained by the H + CO → HCO reaction. The growth in the DOCO concentration after photolysis is therefore taken as strong indirect evidence for the reaction H + DCOOD → HD + DOCO.…”

Section: Experimental and Resultsmentioning

confidence: 99%

“…One of the first research groups to study pure tunneling reactions focused on creating H atoms in solid molecular hydrogen (SMH). − These are fascinating chemical systems due to the importance of nuclear quantum effects; the light mass of the H atom results in a large de Broglie wavelength, and the H 2 molecule undergoes both large amplitude translational zero-point motions and free rotation within SMH . Through a series of radiolysis and photolysis studies of solid H 2 –D 2 mixtures and solid HD, Miyazaki and his group (followed by Kumada) used electron spin resonance (ESR) spectroscopy to demonstrate a number of nonstandard chemical phenomena: (1) H atoms readily diffuse through SMH even at temperatures below 5 K by repeated H + H 2 → H 2 + H tunneling exchange reactions, (2) D atoms produced in solid H 2 rapidly react with the host thereby trapping the D atom in HD and creating mobile H atoms, and (3) H atoms in solid H 2 are remarkably stable on the time scale of hours due presumably to inefficient H + H → H 2 recombination in enriched parahydrogen crystals. − Proof of the importance of tunneling in the measured reaction dynamics is provided by comparison of the rate constant for the D + HD → H + D 2 reaction estimated experimentally to be 3.5 × 10 –27 cm molecule –1 s –1 at 4.2 K with the thermally activated rate constant calculated to be 10 –400 cm 3 molecule –1 s –1 . Further proof the reaction occurs exclusively through tunneling is provided by measuring the rate constants for different isotopic variants of this reaction.…”

Section: Introductionmentioning

confidence: 99%

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Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies

Wonderly

Anderson

2014

J. Phys. Chem. A

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It is difficult to determine whether the measured rate constant for reaction of atomic hydrogen with formic acid reported in Part 1 reflects the H atom quantum diffusion rate or the rate constant for the tunneling reaction step. In Part 2 of this series, we present kinetic studies of the postphotolysis H atom reactions with deuterated formic acid (DCOOD) to address this ambiguity. Short duration 193 nm in situ photolysis of DCOOD trapped in solid parahydrogen results in partial depletion of the DCOOD precursor and photoproduction of primarily CO, CO2, DOCO, HCO and mobile H atoms. At 1.9 K we observe post-irradiation growth in the concentrations of DOCO and HCO that can be explained by H atom tunneling reactions with DCOOD and CO, respectively. Conducting experiments with different deuterium isotopomers of formic acid (DCOOD, DCOOH, HCOOD and HCOOH) provides strong circumstantial evidence the reaction involves H atom abstraction from the alkyl group of formic acid. Further, the anomalous temperature dependence measured for the H + HCOOH reaction in Part 1 is also observed for the analogous reactions with deuterated formic acid. The rate constants extracted for H atom reactions with DCOOD and HCOOH are equivalent to within experimental uncertainty. This lack of a kinetic isotope effect in the measured rate constant is interpreted as evidence the reactions are diffusion limited; the measured rate constant reflects the H atom diffusion rate and not the tunneling reaction rate. Whether or not H atom reactions with chemical species in solid parahydrogen are diffusion limited is one of the outstanding questions in this field, and this work makes significant strides toward showing the reaction kinetics with formic acid are diffusion limited.

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Section: Experimental and Resultsmentioning

confidence: 99%

Section: Experimental and Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies

Wonderly

Anderson

2014

J. Phys. Chem. A

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Matrix photochemistry of nitrosyl chloride.

Hallou¹,

Schriver‐Mazzuoli²,

Schriver³

et al. 1998

Chemical Physics

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Tunneling chemical reactions D+H2→DH+H and D+DH→D2+H in solid D2–H2 and HD–H2 mixtures: An electron-spin-resonance study

Kumada

2006

The Journal of Chemical Physics

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Tunneling chemical reactions D + H2 --> DH + H and D + DH --> D2 + H in solid HD-H2 and D2-H2 mixtures were studied in the temperature range between 4 and 8 K. These reactions were initiated by UV photolysis of DI molecules doped in these solids for 30 s and followed by measuring the time course of electron-spin-resonance (ESR) intensities of D and H atoms. ESR intensity of D atoms produced by the photolysis decreases but that of H atoms increases with time. Time course of the D and H intensities has the fast and slow processes. The fast process, which finishes within approximately 300 s after the photolysis, is assigned to the reaction of D atom with one of its nearest-neighboring H2 molecules, D(H2)n(HD)(12-n) --> H(H2)(n-1)(HD)(13-n) or D(H2)n(D2)(12-n) --> H(HD)(H2)(n-1)(D2)(12-n) for 12 > or = n > or = 1. Rate constant for the D + H2 reaction between neighboring D atom-H2 molecule pair is determined to be (7.5 +/- 0.7) x 10(-3) s(-1) in solid HD-H2 and (1.3+/-0.3) x 10(-2) s(-1) in D2-H2 at 4.1 K, which is very close to that calculated based on the theory of chemical reaction in gas phase by Hancock et al. [J. Chem. Phys. 91, 3492 (1989)] and Takayanagi and Sato [J. Chem. Phys. 92, 2862 (1990)]. This rate constant was found to be independent of temperature up to 7 K within experimental error of +/-30%. The slow process is assigned to the reaction of D atom produced in a cage fully surrounded by HD or D2 molecules, D(HD)12 or D(D2)12. This D atom undergoes the D + DH reaction with one of its nearest-neighboring HD molecules in solid HD-H2 or diffuses to the neighbor of H2 molecules to allow the D + H2 reaction in solid HD-H2 and D2-H2. The former is the main channel in solid HD-H2 below 6 K where D atoms diffuse very slowly, whereas the latter dominates over the former above 6 K. Rate for the reactions in the slow process is independent of temperature below 6 K but increases with the increase in temperature above 6 K. We found that the increase is due to the increase in hopping rate of D atoms to the neighbor of H2 molecules. Rate constant for the D + DH reaction was found to be independent of temperature up to 7 K as well.

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Time evolution of the rate constant for the tunneling reaction H2 + D → H + HD in solid D2H2 mixtures at very low temperature

Cited by 4 publications

References 7 publications

Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies

Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies

Matrix photochemistry of nitrosyl chloride.

Tunneling chemical reactions D+H2→DH+H and D+DH→D2+H in solid D2–H2 and HD–H2 mixtures: An electron-spin-resonance study

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