Radiation Chemistry of Organic Liquids: Saturated Hydrocarbons

Shkrob, Ilya A.; Sauer, Myran C.; Trifunac, A. D.

doi:10.1002/chin.200451258

Cited by 3 publications

(4 citation statements)

References 104 publications

(483 reference statements)

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“…To our knowledge, even for polyethylene, which is the most studied aliphatic polymer, there are no reports of EPR signals that could be attributed to the primary RCs resulting directly from the ionization of the polymer matrix. Similar to the RCs in liquid or frozen alkanes, the primary RCs in polyethylene are typically considered to be unobservable because of the rapid proton transfer from a polymer RC to the surrounding molecules. − …”

Section: Introductionmentioning

confidence: 99%

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

2019

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The delayed radiation-induced fluorescence from polyethylene and its alkyl-and fluorine-substituted analogues doped with aromatic luminophores was studied in the time range of 1−1000 ns. Qualitative analysis of the effects of a magnetic field on the fluorescence decay indicated that, in all polyolefins studied, the main portion of the fluorescence observed arose from the recombination of geminate spincorrelated radical ion pairs (RIPs). In the case of polyethylene, this conclusion was supported by observing the effect of an external electric field on the fluorescence decay. It was shown by comparison with the computer simulation of intratrack recombination that the tunneling character of the RIP recombination, which had an asymptotic time dependence of the geminate recombination rate close to t −1 , was typical of most studied polyolefins at temperatures below 273 K in the time range studied. The increase to room temperature and above caused a gradual transition to a regime where the geminate recombination rate was mainly determined by the migration of RIP partners with time dependence close to t −3/2 . The low estimate of the electron transfer distance upon the ion recombination in this regime was about 2 nm. In polyethylenes, exposed to an irradiation of 0.3−0.4 MGy, the role of charge carrier diffusion became hardly noticeable because of the cross-linking of polyethylene chains and the increase in polymer matrix stiffness. Oxygen, dissolved in a polymer doped with aromatic molecules, caused quenching of the recombination luminescence due to electron transfer from the dopant radical anion to the oxygen molecules. At room temperature, typical distances for such electron transfer were estimated to be ∼1.5 nm.

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Section: Introductionmentioning

confidence: 99%

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

2019

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“…A key step in this process is the recombination of the generated radical ion pair via electron transfer from a radical anion to a radical cation that releases sufficient energy to produce electronically excited states of the solute. 1,2 Radical ion pair recombination can also lead to the formation of excited state complexes (exciplexes) between the parent molecules of the radical ion pair, due to the close proximity of the excited molecule and its partner. In the case of X-radiation, exciplexes could be obtained for systems with an extremely short lifetime of the excited state of the employed electron acceptor.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the fluorescence lifetime for optically inaccessible exciplexes in nonpolar solutions under ionizing irradiation

Melnikov

Kalneus

Korolev

et al. 2016

Photochem Photobiol Sci

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X-irradiation of nonpolar solutions likely provides a possibility to create exciplexes for any donor-acceptor pair that would energetically and sterically allow this. Thorough study and characterization of X-radiation generated exciplexes usually cannot be carried out with conventional methods because of the complex and non-exponential formation and decay dynamics of these species. In this paper, we present a simple and universal experimental approach for the estimation of fluorescence lifetimes (τF) of X-radiation generated exciplexes. The suggested procedure is based on the comparison of quenching of the exciplex emission band and the emission band from a standard luminophore with a known excited state lifetime by dissolved oxygen. Using this approach we report the τF values for two systems with optically inaccessible exciplexes, diphenylacetylene-N,N-dimethylaniline (DMA) and p-terphenyl-DMA, and for two typical exciplex forming systems, naphthalene-DMA and anthracene-DMA. All the found τF values for the X-radiation generated exciplexes lie in the range of 50-70 ns. The accuracy of this approach was checked by time-resolved measurements under X- or near-UV irradiation for those pairs, whose properties make this feasible. The proposed method gives a possibility to avoid a complex numerical evaluation of the non-exponential kinetics of recombination luminescence, and can be used to estimate the characteristic τF values for luminophores and excited complexes formed under X-radiation.

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“…Such recombination will result in the formation of electronically excited states of aliphatic polyolefin molecules, the decay of which can lead to a very rapid cleavage of C−C bonds and the formation of neutral alkyl radicals. 37 If, to the contrary, all primary RCs decompose into non-RCs, then the fast recombination with electrons should also result in the formation of neutral alkyl radicals.…”

Section: Resultsmentioning

confidence: 99%

“…If the excess electron mobility in PIB is comparable to those in branched alkanes, which is very high, then most of the primary ion pairs will recombine within the subnanosecond time range. Such recombination will result in the formation of electronically excited states of aliphatic polyolefin molecules, the decay of which can lead to a very rapid cleavage of C–C bonds and the formation of neutral alkyl radicals . If, to the contrary, all primary RCs decompose into non-RCs, then the fast recombination with electrons should also result in the formation of neutral alkyl radicals.…”

Section: Resultsmentioning

confidence: 99%

Primary Radical Cations in Irradiated Poly(isobutylene)

et al. 2020

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Using the method of time-resolved magnetic field effect in radiation-induced fluorescence, primary radical cations (RCs) in irradiated poly(isobutylene) (PIB) have been detected for the first time. A comparison of experimental results with the data of quantum chemical calculations suggests that the initial geometry of the ionized fragment of the PIB molecule is close to the geometry of the neutral polymer in the trans–gauche–trans–gauche conformation. The spin density of the RC in this geometry is delocalized over more than 10 polymer units, and the width of the RC’s EPR spectrum is about ΔH pp ≈ 1.3 mT. At a temperature of 273 K and lower, the lifetime of the primary RCs with the delocalized spin density exceeds 10 ns. The structural relaxation of the RCs results in the spin density localization on a single C–C bond, which is extended to nearly 0.2 nm, and in the increase in the EPR spectrum width to ΔH pp ≈ 2.4 mT. It looks likely that this intramolecular structural relaxation is coupled strongly with those types of molecular motions that determine the process of dielectric β-relaxation in the polymer.

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Radiation Chemistry of Organic Liquids: Saturated Hydrocarbons

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 3 publications

References 104 publications

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

Estimation of the fluorescence lifetime for optically inaccessible exciplexes in nonpolar solutions under ionizing irradiation

Primary Radical Cations in Irradiated Poly(isobutylene)

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