Some remarks about free radicals and the photochemistry of solutions

Franck, J.; Rabinowitsch, E.

doi:10.1039/tf9343000120

Cited by 506 publications

(240 citation statements)

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“…In order to obtain quantitative information about the quantum yield of cumyl radicals and its dependence on an external magnetic field, the dependence on time of the optical density at 329 nm was measured for magnetic fields between 0.02 and 2.94 T, using solutions of 1. because of the decrease of the radical quantum yield via direct photolysis in more viscous solvents, due to the so called "cage effect" [54]. This decrease is in agreement with literature data concerning the "cage effect" for AC [55].…”

Section: Quantum Yield Of Cumyl Radicals and Magnetic Field Effectsupporting

confidence: 90%

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

Milikisiyants

Steiner

Paul³

2011

Appl Magn Reson

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The triplet-sensitized photodecomposition of azocumene into nitrogen and cumyl radicals is investigated by time-resolved electron paramagnetic resonance and absorption spectroscopy. The radicals are found to be created spin polarized with a yield depending on the strength of the applied magnetic field. The phenomenon arises because in triplet azocumene, the decay into radicals competes with a fast triplet-sublevel selective intersystem crossing back to the azocumene ground state. The size of the initial spin polarization of the radicals and the magnetic field effect on their yield are determined in solvents of different viscosities. Data analysis yields rate constants for the intersystem crossing and the cleavage reaction of triplet azocumene as well as its zero-field splitting D ZFS. At room temperature in nonpolar solvents, the most probable values are: k x = k y = 1.2 × 1011 s−1 and k z = 1.9 × 1010 s−1 for the intersystem crossing from the energetically lower and upper triplet substates, respectively, k p = 1.6 × 109 s−1 for the cleavage reaction and for the zero-field splitting D ZFS = −3.4 × 1010 s−1 (0.18 cm−1).

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Section: Quantum Yield Of Cumyl Radicals and Magnetic Field Effectsupporting

confidence: 90%

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

Milikisiyants

Steiner

Paul³

2011

Appl Magn Reson

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“…This phase difference is a commonly observed phenomenon in radiolysis and is attributed to the cage effect (Franck & Rabinowitsch 1934;Johnson et al 1992), where dissociation products scatter with surrounding molecules in the solid (the cage) giving a high probability of recombination.…”

Section: Comparison Of Photolysis and Ion-induced Radiolysismentioning

confidence: 99%

CO$\mathsf{_{2}}$ synthesis in solid CO by Lyman-α photons and 200 keV protons

Loeffler

Baratta²,

Palumbo³

et al. 2005

A&A

138

150

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Abstract.We have studied the synthesis of carbon dioxide from solid carbon monoxide at 16 K induced by photolysis with Lyman-α photons and by irradiation with 200 keV protons to quantitatively compare the effects of photolysis and ion irradiation on CO ice and to determine the importance of these processes in interstellar ice grains. The CO and CO 2 concentrations during irradiation of an initially pure CO film evolve with fluence to a saturation value, a behaviour that is explained by a two-state model. Our results indicate that the initial CO 2 production rates for both radiation processes are similar when normalized to the absorbed energy and that the solid CO 2 abundance observed in the interstellar ices cannot be explained only by radiolysis and photolysis of pure solid CO.

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“…The matrix cage will also increase the dissociation threshold energy which can be detected by a decrease of the photodissociation yield. 34 In the case of recombination of the photofragments of O 2 , the 3 ⌬ u electronic level will be populated and visible ͑vis͒ radiative decay to the 3 ⌺ g − ground state will be observed. The fluorescence of this transition will be taken as an indicator for inhibited dissociation.…”

Section: A General Remarksmentioning

confidence: 99%

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

Laarmann

Wabnitz

Haeften

et al. 2008

The Journal of Chemical Physics

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The caging effect of the host environment on photochemical reactions of molecular oxygen is investigated using monochromatic synchrotron radiation and spectrally resolved fluorescence. Oxygen doped clusters are formed by coexpansion of argon and oxygen, by pickup of molecular oxygen or by multiple pickup of argon and oxygen by neon clusters. Sequential pickup provides radially ordered core-shell structures in which a central oxygen molecule is surrounded by argon layers of variable thickness inside large neon clusters. Pure argon and core-shell argon-neon clusters excited with ϳ12 eV monochromatic synchrotron radiation show strong fluorescence in the vacuum ultraviolet ͑vuv͒ spectral range. When the clusters are doped with O 2 , fluorescence in the visible ͑vis͒ spectral range is observed and the vuv radiation is found to be quenched. Energy-resolved vis fluorescence spectra show the 2 1 ⌺ + → 1 1 ⌺ + ͑ArO͑ 1 S͒ → ArO͑ 1 D͒͒ transition from argon oxide as well as the vibrational progression A Ј 3 ⌬ u ͑ Ј=0͒ → X 3 ⌺ g − ͑ Љ͒ of O 2 indicating that molecular oxygen dissociates and occasionally recombines depending on the experimental conditions. Both the emission from ArO and O 2 as well the vuv quenching by oxygen are found to depend on the excitation energy, providing evidence that the energy transfer from the photoexcited cluster to the embedded oxygen proceeds via the O 2 + ground state. The O 2 + decays via dissociative recombination and either reacts with Ar resulting in electronically excited ArO or it recombines to O 2 within the Ar cage. Variation of the Ar layer thickness in O 2 -Ar-Ne core-shell clusters shows that a stable cage is formed by two solvation layers.

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Some remarks about free radicals and the photochemistry of solutions

Cited by 506 publications

References 0 publications

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

CO$\mathsf{_{2}}$ synthesis in solid CO by Lyman-α photons and 200 keV protons

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

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