Photosensitized aquation reactions of Cr(NH3 5(NCS)2+

Biacetyl and acridinium ion but not Michler's ketone sensitize the aquation of Cr(NH_{3 5}(NCS)²⁺ in 0.1 N sulfuric acid solution. Phosphorescence quenching occurs in first system, and the kinetics of this and of the sensitized reaction in the presence and absence of oxygen indicate that transfer of excitation energy occurs from the biacetyl first triplet state. The reaction is entirely one of ammonia aquation, indicating that the first quartet excited state of the complex is populated.Acridinium ion sensitizes both ammonia and thiocyanate aquation, the presence of oxygen affecting the latter but not the former mode. The kinetics of the fluorescence quenching by the complex and that of the sensitized ammonia aquation indicate that the latter process is induced by the first singlet excited state of acridinium ion, along with a small component of thiocyanate aquation. The oxygen dependence results indicate that the remainder of the thiocyanate aquation is induced by the first triplet excited state of the donor. It is concluded that, in this system, the singlet excited state of acridinium ion populates the first quartet excited state of the complex ion while the triplet state populates the doublet excited state of the complex. Some of the complexities of excited state processes of Cr(III) complexes are discussed.

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Zusammenfassung Das Biacetyl und das Acridinium, nicht aber Michler's Keton sensibilisieren die Aquotisierung von Cr(NH_{3 5}(NCS)²⁺ in 0,1 n-Schwefelsäure-Lösung. Phosphoreszenzlöschung tritt im erstgenannten System auf und seine Kinetik, sowie die der sensibilisierten Reaktion, in Gegenwart sowie unter Ausschluß von Sauerstoff weist darauf hin, daß der Übergang der Anregungsenergie vom ersten Triplettzustand des Biacetyls stattfindet. Die Reaktion führt anschließend zur Aquotisierung von Ammoniak. Diese Tatsache weist darauf hin, daß der erste angeregte Quartettzustand des Komplexes besetzt wird. Das Acridinium sensibilisiert sowohl die Ammoniakals auch die Thiocyanat-Aquotisierung, wobei die Gegenwart von Sauerstoff zwar letztere, jedoch nicht erstere beeinflußt. Die Kinetik der Fluoreszenzlöschung durch den Komplex sowie die der sensibilisierten Ammoniak-Aquotisierung deuten darauf hin, daß letzterer Prozeß durch den ersten angeregten Singulettzustand des Acridiniums induziert wird, zusammen mit einem kleinen Teil der Thiocyanat-Aquotisierung. Die Sauerstoffabhängigkeit zeigt, daß der Rest der Thiocyanat-Aquotisierung durch den ersten angeregten Triplettzustand des Donors induziert wird. Daraus wird der Schluß gezogen, daß in diesem System der angeregte Singlettzustand des Acridiniums zur Besetzung des ersten angeregten Quartettzustands des Komplexes führt, wohingegen die Energie des Triplettzustands auf den angeregten Dublettzustand des Komplexes übertragen wird. Einige Probleme der Prozesse zwischen angeregten Zuständen von Cr(III)-Komplexen werden diskutiert.

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Résumé Les ions biacétyle et acridinium, mais non pas la cétone de Michler, sensibilisent l'hydratation de Cr(NH₃)₅(NCS)²⁺ dans une solution d'acide sulforique 0,1 N. L'extinction de la phosphorescence se produit dans le premier système; sa cinétique ainsi que celle de la réaction sensibilisée en présence et en l'absence d'oxygène indiquent que le transfert d'énergie d'excitation se produit à partir du premier état triplet du biacétyle. La réaction est totalement celle de l'hydratation de l'ammoniac, ce qui indique que le premier quartet excité du complexe se trouve peuplé.L'ion acridinium sensibilise l'hydratation de l'ammoniac et du thiocyanate seule cette dernière réaction étant sensible à l'oxygène. La cinétique de l'extinction de fluorescence par le complexe ainse que celle de l'hydratation sensibilisée de l'ammoniac indiquent que ce dernier processus est induit par le premier état excité singulet de l'ion acridinium, avec parallèlement une faible hydratation du thiocyanate. Les résultats sur le rôle de l'oxygène montrent que le restant de l'hydratation du thiocyanate est induit par le premier triplet excité du donneur. On en conclue que dans ce système l'état excité singulet de l'ion acridinium peuple le premier quartet excité de l'ion complexe tandis que l'état triplet peuple l'état excité doublet du complexe. On discute certains détails complexes des processus d'excitation des complexes de Cr (III).

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Dedicated to the memory of Professor Hans-Ludwig Schläfer.     

A novel example of chiral counteranion induced enantioselective metal catalysis: the importance of ion-pairing in copper-catalyzed olefin aziridination and cyclopropanation

A new ion-pairing route to achieve asymmetric catalysis has been observed in the copper-catalyzed aziridination of styrene with a chiral counteranion. Structural studies suggest that enantioinduction occurs via ion-pairing of the cationic copper catalyst in the chiral pocket created by the anion. The degree of asymmetric induction can be tuned with features that affect ion-pairing, such as achiral and chiral ligands, temperature, and solvent polarity.     

The influence of a multilayer system of inhomogeneous ultrathin films on reflection of light from dielectric materials

Optics and Spectroscopy - The influence of surface layers on reflection of light in the absence of absorption is studied. The contribution of an ultrathin N-layer film system to the light...     

Laser stimulation of low-temperature dissociative recombination of electrons and oxygen molecular ions

A theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e^? + O ₂ ⁺ (²Π _g ) → $ O(^{2s_1 + 1} l_1 ) + O(^{2s_2 + 1} l_2 ) A theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e⁻ + O₂⁺(²Π _g ) → reaction is analyzed. A study of this reaction requires detailed information about the potential curves of the states participating in it with taking into account the external electromagnetic field (l and s are the electronic angular momenta and reaction product spins). For this purpose, the general problem is divided into three stages. At the first stage, the theoretical approach is formulated, and at the second stage, the corresponding potential curves are calculated and the main reaction mechanisms are determined. The third stage should include calculations of the total and differential cross sections. This work is concerned with the first two stages; that is, the adiabatic potential curves of the singlet and triplet dissociative states of the O₂^** oxygen molecule are calculated, a classification of all possible transition types is given, and reaction mechanisms in the presence of monochromatic laser radiation are determined. The frequency regions of external radiation in which these mechanisms are most effective are found. Original Russian Text ? S.O. Adamson, R.J. Buenker, G.V. Golubkov, M.G. Golubkov, A.I. Dement’ev, 2009, published in Khimicheskaya Fizika, 2009, Vol. 28, No. 4, pp. 26–42.     

Potential Energies of the Orbitally Degenerate Atmospheric Rydberg Complexes

A method was developed for calculating the vibronic potential energy surfaces (PESs) of atmospheric complexes consisting of orbitally degenerate Rydberg nitrogen and oxygen molecules and the molecules of a neutral medium in the ground electronic state. The degenerate states are formed as a result of l-mixing in the D and E layers of the atmosphere during the periods of increased solar activity. The complexes are populated in the nonequilibrium two-temperature plasma and are responsible for the incoherent additional background radiation in the decimeter (microwave) and terahertz (IR) bands at an altitude of 80–110 km from the Earth’s surface. To describe the interaction of a weakly bound electron with a singly charged molecular ion and a neutral molecule of a gas medium, the formalism of the multichannel quantum defect (MCD) theory was used. Quantum-chemical calculations of the dependences of the scattering lengths, polarizabilities, and quadrupole moments of the main atmospheric molecules N₂ and O₂ on the interatomic distance were performed. The specific features of the behavior of vibronic PESs of Rydberg complexes for large values of the principal quantum number (n ? 1) were analyzed. The vibronic PESs of orbitally degenerate states were constructed. They are necessary for determining the positions and shape of the vibronic minima of the l-mixing cross sections of the N₂ and O₂ Rydberg molecules in the D and E layers of the Earth’s atmosphere, where the delay times of satellite positioning signals should be minimum. The possibility of “quantum chaos” appearing in the Rydberg complexes at sufficiently large n values and angular momenta of the weakly bound electron was noted.     

Adsorptions- und Kontaktwinkel-Studien. II. Wasser und organische Substanzen an poliertem Polytetrafluoräthylen

Ohne Zusammenfassung