Detection of free radicals in low-temperature gas-grain reactions
of astrophysical interest

Zhitnikov, R. A.; Dmitriev, Yu. A.

doi:10.1051/0004-6361:20020268

Cited by 42 publications

(34 citation statements)

References 21 publications

(53 reference statements)

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“…The experimental technique and a schematic of the setup have been presented elsewhere (e. g., [12]). …”

Section: Resultsmentioning

confidence: 99%

EPR spectra of deuterated methyl radicals trapped in low temperature matrices

Dmitriev

2005

Low Temperature Physics

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EPR spectra of CHD 2 , and CD 3 radicals have been investigated in low-temperature matrices of H 2 , D 2 , and Ne at temperatures 1.6-4.2 K. A method of condensation from the gas phase on a cold substrate has been used. With decreasing sample temperature, a transformation of the shape of the CD 3 spectrum in H 2 , D 2 , and Ne matrices and CHD 2 spectrum in H 2 and Ne was observed. This transformation was reversible in the above temperature range. The temperature effects are explained as reflecting a change in the populations of the lowest rotational states of the radicals. Based on the present data and known results for deuterated methyl radicals in Ar obtained in photolytic experiments, we compare the temperature behavior of the EPR spectra for the radicals trapped in various matrices. As a result an existence of a hindering barrier for the radical rotation is suggested.

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“…The experimental technique and a schematic of the setup have been presented elsewhere (e. g., [12]). …”

Section: Resultsmentioning

confidence: 99%

EPR spectra of deuterated methyl radicals trapped in low temperature matrices

Dmitriev

2005

Low Temperature Physics

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“…free radicals) due to the gas discharge products. A scheme of the experimental set-up has been presented in previous papers [11].…”

Section: Resultsmentioning

confidence: 99%

EPR spectra and rotation of CH3, CH2D, CHD2, and CD3 radicals in solid H2

Dmitriev¹,

Zhitnikov²

2003

Low Temperature Physics

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EPR spectra of CH 3 , CH 2 D, CHD 2 , and CD 3 radicals have been observed in H 2 matrix in the temperature range 1.6-4.2 K. The radicals were obtained by condensation on a cold substrate of two gas flows: deuterium mixed with 2 mol % methane passed through a discharge and pure hydrogen avoiding the discharge. The CD 3 and CHD 2 spectra were found to be a superposition of two spectra: high-temperature and low-temperature. A transformation of the shape of CD 3 and CHD 2 spectrum with decreasing sample temperature was observed. This is attributed to a change in the populations of the lowest rotational states of the radicals. Compared to known results for deuterated methyl radicals in Ar, the present observations suggest an existence of a hindering barrier for the radical rotation in solid H 2 .

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“…that at 10 K the methyl radicals are predicted not to be mobile within the lattice (Zhitnikov & Dmitriev 2002). The hydrogen atoms, on the other hand, can diffuse even at temperatures as low as 10 K and can recombine to form molecular hydrogen,…”

Section: Energeticsmentioning

confidence: 97%

Laboratory Studies on the Irradiation of Methane in Interstellar, Cometary, and Solar System Ices

Bennett

Jamieson

Osamura

et al. 2006

ApJ

156

168

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Pure methane ices (CH 4 ) were irradiated at 10 K with energetic electrons to mimic the energy transfer processes that occur in the track of the trajectories of MeV cosmic-ray particles. The experiments were monitored via an FTIR spectrometer (solid state) and a quadrupole mass spectrometer (gas phase). Combined with electronic structure calculations, this paper focuses on the identification of CH x (x ¼ 1Y4) and C 2 H x (x ¼ 2Y6) species and also investigates their formation pathways quantitatively. The primary reaction step is determined to be the cleavage of a carbonhydrogen bond of the methane molecule to form a methyl radical (CH 3 ) plus a hydrogen atom. Hydrogen atoms recombined to form molecular hydrogen, the sole species detected in the gas phase during the irradiation exposure. In the matrix two neighboring methyl radicals can recombine to form an internally excited ethane molecule (C 2 H 6 ), which either can be stabilized by the surrounding matrix or was found to decompose unimolecularly to the ethyl radical (C 2 H 5 ) plus atomic hydrogen and then to the ethylene molecule (C 2 H 4 ) plus molecular hydrogen. The initially synthesized ethane, ethyl, and ethylene molecules can be radiolyzed subsequently by the impinging electrons to yield the vinyl radical (C 2 H 3 ) and acetylene (C 2 H 2 ) as degradation products. Upon warming the ice sample after the irradiation, the new species are released into the gas phase, simulating the sublimation processes interstellar ices undergo during the hot core phase or comets approaching perihelion. Our investigations also aid the understanding of the synthesis of hydrocarbons likely to be formed in the aerosol particles and organic haze layers of hydrocarbon-rich atmospheres of planets and their moons such as Titan.

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Detection of free radicals in low-temperature gas-grain reactions of astrophysical interest

Cited by 42 publications

References 21 publications

EPR spectra of deuterated methyl radicals trapped in low temperature matrices

EPR spectra of deuterated methyl radicals trapped in low temperature matrices

EPR spectra and rotation of CH3, CH2D, CHD2, and CD3 radicals in solid H2

Laboratory Studies on the Irradiation of Methane in Interstellar, Cometary, and Solar System Ices

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