The collison mechanism and the primary photochemical process in solutions

Rabinowitch, Eugene; Wood, William C.

doi:10.1039/tf9363201381

Cited by 165 publications

(80 citation statements)

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“…This seems to be the reason w h~-previous estimates based on a free collision mechanism appeared to lead to reasonable results. The "cage mechanism" proposed here is somewhat similar to the conversion mechanism in liquids where repeated collisions are also assumed to occur (11). The rates found in paramagnetic solutions are nearly equal to those found with paramagnetic gases (8).…”

Section: Discussionsupporting

confidence: 56%

The Ortho–para Conversion of Hydrogen and Deuterium on Inhomogeneous Paramagnetic Surfaces

Sandler¹

1954

Can. J. Chem.

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The kinetics of the magnetic ortho-para conversion of hydrogen and deuterium on neodymium oxalate and heniin crystals has been determined over a wide temperature range in a static system. In these cases a similar type of rate curve is obtained: a t high and a t low temperatures the rate decreases with temperature, while in the intermediate region the rate increases with temperature. The behavior is explained in terms of a n energetic surface heterogeneity. In case of neodymium oxalate two distinctly different groups of sites appear to be active having energy barriers to migration of the adsorbed hydrogen a t considerably different height. The conversion mechanism of the "trapped" gas is assumed to be similar t o the mechanism in liquids where repeated collisions are also assumed to occur. INI'RODUCTION'I'he ortho-para conversion of hydrogen is catalyzed by molecular inhomogeneous magnetic fields (6,14). This type of conversion has been observed to take place in the presence of paramagnetic gases, ions and molecules in solution (6) and when hydrogen is adsorbed on solids (1,13,7,2). The conversion on paramagnetic solids generally proceeds appreciably faster than on diamagnetic solids (13). In the latter case, when a conversion was found* it has been attributed to "surface paramagnetism" (I).When the fraction of gas adsorbed is small, generally a negative temperature coefficient (negative "apparent activation energy") of the conversion has been found. This has been explained as due to a decrease in coverage of the solids with temperature; the negative activation energy found was approximately equal to the expected heat of adsorption of hydrogen on these solids (I). However, Eley (2) reported that with hemin the conversion is approximately temperature independent between + 185°C. and -80°C. He suggested that the adsorbed hydrogen might require an activation energy for approaching the paramagnetic center, in this case fortuitously equal to the heat of adsorption. On the other hand, I,. Farkas and the present author (7) a t the same time reported that with neodymium oxalate the conversion appears to have the normal temperature dependence above O0C., while below this temperature the apparent activation energy becomes strongly positive.In order to obtain more information on the nature of the activation energies in these two interesting cases it seemed desirable to investigate the kinetics of the conversion on hemin and neodymium oxalate more thoroughly than has been done heretofore.' Ma~zz~script

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Section: Discussionsupporting

confidence: 56%

The Ortho–para Conversion of Hydrogen and Deuterium on Inhomogeneous Paramagnetic Surfaces

Sandler¹

1954

Can. J. Chem.

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“…This reaction occurs due to collisions of dissociating I 2 molecule with surrounding solvent molecules, whereby the vibrational kinetic energy of the I 2 molecule is dissipated as the molecule reaches thermal equilibrium 119–121 . The dynamics of vibrational energy dissipation has been well characterized by spectroscopic studies of the photodissociation and subsequent recombination of I 2 in CCl 4 , alkane liquids, and noble gas matrices 111–118,127–131 .…”

Section: Geminate Recombination and Vibrational Cooling Of Molecular mentioning

confidence: 99%

Topical Review: Molecular reaction and solvation visualized by time-resolved X-ray solution scattering: Structure, dynamics, and their solvent dependence

Kim

Lee

et al. 2014

Structural Dynamics

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Time-resolved X-ray solution scattering is sensitive to global molecular structure and can track the dynamics of chemical reactions. In this article, we review our recent studies on triiodide ion (I3–) and molecular iodine (I2) in solution. For I3–, we elucidated the excitation wavelength-dependent photochemistry and the solvent-dependent ground-state structure. For I2, by combining time-slicing scheme and deconvolution data analysis, we mapped out the progression of geminate recombination and the associated structural change in the solvent cage. With the aid of X-ray free electron lasers, even clearer observation of ultrafast chemical events will be made possible in the near future.

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“…Only certain balls were made of conducting material and ªcollisional hitsº were observed from these balls. [36] The ªcollisionsº of molecules in a solvent were ªsimulatedº by this mechanical device. From this device the authors concluded that collisions between molecules that are nearest neighbors in a solvent cage occur in sets.…”

Section: The Cage Effectðfrom the Gas Phase To The Molecular Solvent mentioning

confidence: 99%

Electron Spin Polarization and Time-Resolved Electron Paramagnetic Resonance: Applications to the Paradigms of Molecular and Supramolecular Photochemistry

Turro

Kleinman

Karatekin

2000

Angew. Chem. Int. Ed.

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Most molecular and supramolecular organic photochemical reactions involve paramagnetic reactive intermediates (such as molecular triplet states, triplet radical pairs, and free radicals). In a number of cases these species are created with “anomalous” spin populations which are far from thermal equilibrium. Such paramagnetic species are said to be “spin polarized” and may be observed directly by time‐resolved electron paramagnetic resonance (TREPR). The TREPR technique can be applied to exploit spin polarization, which, in addition to providing an enormous signal to noise enhancement, also reveals the mechanisms involved in photochemical reactions. TREPR spectroscopy provides a means of tracking the reaction of radicals with molecules and the nonreactive interactions of radicals with other radicals in real time. The latter interactions provide a systematic investigation of supramolecular interactions of geminate radicals in micelles.

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The collison mechanism and the primary photochemical process in solutions

Cited by 165 publications

References 0 publications

The Ortho–para Conversion of Hydrogen and Deuterium on Inhomogeneous Paramagnetic Surfaces

The Ortho–para Conversion of Hydrogen and Deuterium on Inhomogeneous Paramagnetic Surfaces

Topical Review: Molecular reaction and solvation visualized by time-resolved X-ray solution scattering: Structure, dynamics, and their solvent dependence

Electron Spin Polarization and Time-Resolved Electron Paramagnetic Resonance: Applications to the Paradigms of Molecular and Supramolecular Photochemistry

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