DOI: 10.1063/1.438508. ESR studies of irradiated methane and ethane at 4.2 K and mechanism of pairwise trapping of radicals in irradiated alkanes

ESR studies of irradiated methane and ethane at 4.2 K and mechanism of pairwise trapping of radicals in irradiated alkanes

10.1063/1.438508

Crossref journal-article

AIP Publishing

The Journal of Chemical Physics (317)

Abstract

The spatial distributions of trapped hydrogen atoms and methyl radicals in CH4 and CD4 irradiated at 4.2 K have been studied by ESR. Most of the hydrogen atoms are trapped within ∼16 Å from each parent methyl radical forming distributed radical pairs. This indicates that the thermalization distance of hydrogen atoms produced by 4.2 K radiolysis is ≲16 Å in methane. Evidence has been obtained for the formation of a small amount of ĊH3...ĊH3 pairs, which are supposedly formed from hot hydrogen atom reactions. No evidence has been obtained for the formation of a pair of hydrogen atoms. There has been also obtained the experimental evidence that thermal hydrogen atoms unreactive with methane can abstract a hydrogen atom from ethane at 10–20 K. In the light of these results, the following conclusions are deduced: A part of hydrogen atoms produced in radiolysis of alkanes undergo hot abstraction to form very close alkyl radical pairs whereas the rest is thermalized and immobilized at the place close to each parent alkyl radical. The thermalized hydrogen atoms also abstract a hydrogen atom from the surrounding molecules to form distributed alkyl radical pairs, when the matrix molecule is reactive with thermal hydrogen atoms. On the other hand, the hydrogen atoms are mobile at elevated temperatures and the isolated alkyl radicals are mainly formed.

Bibliography

Toriyama, K., Iwasaki, M., & Nunome, K. (1979). ESR studies of irradiated methane and ethane at 4.2 K and mechanism of pairwise trapping of radicals in irradiated alkanes. The Journal of Chemical Physics, 71(4), 1698â1705.

Authors 3

Kazumi Toriyama (first)
Machio Iwasaki (additional)
Keichi Nunome (additional)

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Dates

Type	When
Created	22 years, 5 months ago (Feb. 27, 2003, 4:39 p.m.)
Deposited	1 year, 6 months ago (Feb. 9, 2024, 3:20 p.m.)
Indexed	1 year, 6 months ago (Feb. 11, 2024, 3:18 a.m.)
Issued	46 years ago (Aug. 15, 1979)
Published	46 years ago (Aug. 15, 1979)
Published Print	46 years ago (Aug. 15, 1979)

Funders 0

None

BibTeX

@article{Toriyama_1979, title={ESR studies of irradiated methane and ethane at 4.2 K and mechanism of pairwise trapping of radicals in irradiated alkanes}, volume={71}, ISSN={1089-7690}, url={http://dx.doi.org/10.1063/1.438508}, DOI={10.1063/1.438508}, number={4}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Toriyama, Kazumi and Iwasaki, Machio and Nunome, Keichi}, year={1979}, month=aug, pages={1698–1705} }

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  "abstract": "<jats:p>The spatial distributions of trapped hydrogen atoms and methyl radicals in CH4 and CD4 irradiated at 4.2 K have been studied by ESR. Most of the hydrogen atoms are trapped within \u223c16 \u00c5 from each parent methyl radical forming distributed radical pairs. This indicates that the thermalization distance of hydrogen atoms produced by 4.2 K radiolysis is \u227216 \u00c5 in methane. Evidence has been obtained for the formation of a small amount of \u010aH3...\u010aH3 pairs, which are supposedly formed from hot hydrogen atom reactions. No evidence has been obtained for the formation of a pair of hydrogen atoms. There has been also obtained the experimental evidence that thermal hydrogen atoms unreactive with methane can abstract a hydrogen atom from ethane at 10\u201320 K. In the light of these results, the following conclusions are deduced: A part of hydrogen atoms produced in radiolysis of alkanes undergo hot abstraction to form very close alkyl radical pairs whereas the rest is thermalized and immobilized at the place close to each parent alkyl radical. The thermalized hydrogen atoms also abstract a hydrogen atom from the surrounding molecules to form distributed alkyl radical pairs, when the matrix molecule is reactive with thermal hydrogen atoms. On the other hand, the hydrogen atoms are mobile at elevated temperatures and the isolated alkyl radicals are mainly formed.</jats:p>",
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