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Charles L. Braun - One of the best experts on this subject based on the ideXlab platform.
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Solvent-Separated Radical Ion Pairs and Free Ion Yields. 1. Effect of Temperature on Free Ion FormatIon in SolutIon
The Journal of Physical Chemistry A, 2004Co-Authors: Cheng Zhong, Jinwei Zhou, Charles L. BraunAbstract:Free Ion yields from geminate Ion pairs formed after photoinduced electron transfer are measured by the transient photocurrent method in three moderately polar solvents. Photoexcited 9,10-dicyanoanthracene (DCA) is used as the electron acceptor and alkyl-substituted benzenes as donors. It was found that, generally, there is no significant change in Free Ion yield as the temperature is increased. On the basis of a theoretical model developed under Collins−Kimball boundary conditIons, several factors are analyzed, including dielectric constants and viscosities of solvents, initial separatIon distance distributIon of geminate Ion pairs, and temperature-induced changes in recombinatIon rates. By comparing escape probabilities of geminate Ion pairs calculated at different initial formatIon and recombinatIon/separatIon distances with measured Free Ion yields, we show that Free Ions are mainly produced from the solvent-separated Ion pairs that are initially formed after electron transfer quenching of photoexcite...
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Long distance photoinduced electron transfer in solutIons: A mechanism for producing large yields of Free Ions by electron transfer quenching
The Journal of Physical Chemistry A, 2002Co-Authors: Jinwei Zhou, Roshan P. Shah, Bret R. Findley, Charles L. BraunAbstract:Free Ion and fluorescence quantum yields from the geminate Ion pairs formed by electron-transfer quenching of the excited acceptor 9,10-dicyanoanthracene by aromatic electron-donors are measured in different solvents. Theeffects of solvent polarity, energetic driving force, and steric substitutIon on Free Ion yields are studied. From the comparison of the effect of driving force on Free Ion yields and fluorescence quantum yields in different solvents, especially those of moderate polarity, it is concluded that Free Ion yields are controlled by both recombinatIon rate constants and the separatIon distance distributIon of the initially formed geminate radical Ion pairs. In dichloromethane (DCM), the recombinatIon and Free Ion formatIon processes are directly observed by fluorescence lifetime and transient photocurrent measurements. The time-resolved results indicate that Free Ion formatIon is faster than the recombinatIon process. This means that the geminate radical Ion pairs that form Free Ions and those that are neutralized by electron-transfer recombinatIon have different histories with different separatIon distances. From studies of steric effects on Free Ion yields in different solvents, it is concluded that, in polar solvents such as acetonitrile and butyronitrile, the main effect of steric hindrance is to decrease the recombinatIon rate constant and increase the escape probability, whereas in moderately polar solvents such as tetrahydrofuran, DCM and 1,2-dichlorobenzene, the main effect of steric bulk is to change the initial separatIon distance distributIon of the geminate radical Ion pairs formed by electron-transfer quenching. As an example, we compare donors such as durene (DUR) with those of greater steric bulk like 1,2,4,5-tetra-iso-propylbenzene (TIPB), for which the driving force for electron transfer is similar. The Free radical Ion yield for TIPB is more than 40 times greater than it is for DUR in DCM. This is the first example from our work in which the infinite rate boundary conditIon for Ion recombinatIon used by Onsager is not adequate, because there is no perfect sink at the origin. The Free Ion yield data are analyzed by the theory of Hong and Noolandi under the Collins and Kimball boundary conditIon.
Eric Vauthey - One of the best experts on this subject based on the ideXlab platform.
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DeterminatIon of the Free Ion yield in photoinduced electron transfer processes using transient thermal phase grating spectroscopy
Journal of Photochemistry and Photobiology A: Chemistry, 1995Co-Authors: Arthur Henseler, Eric VautheyAbstract:An applicatIon of transient thermal phase grating spectroscopy with near-infrared probing to the determinatIon of Free Ion yield in photoinduced electron transfer reactIons is presented. The model system is 9,10-dicyanoanthracene with various electron donors in acetonitrile. The measured yields are in good agreement with those obtained from photoconductivity, when the latter are correctly calibrated. The method is explained and its advantages and limitatIons are discussed.
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Marcus inverted regIon: nature of donor–acceptor pairs and Free Ion yields
J. Chem. Soc. Faraday Trans., 1994Co-Authors: D. Burget, P. Jacques, Eric Vauthey, Paul Suppan, Edwin HaselbachAbstract:The Free Ion yield (ΦR) resulting from the fluorescence quenching of 9,10-dicyanoanthracene (DCA) by various electron donors in acetonitrile has been studied using ns laser photoconductivity. The influence of the chemical nature of the doors is established in a general manner. For a given oxidatIon potential Eox(D/D+), the rate constant of geminate Ion recombinatIon, kbac, decreases significantly as the electronic delocalizatIon of the donor increases. As a consequence multiple Marcus plots are observed in the inverted regIon. These plots show decreasing curvature when going from stilbenes to amines as donors. This ‘fan effect’ is tentatively explained by considering the detailed roles of the parameters V, λ and hν in the Marcus model.
Anne-marie Kelterer - One of the best experts on this subject based on the ideXlab platform.
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A theoretical study on trivalent europium: from the Free Ion to the water complex.
The journal of physical chemistry. A, 2014Co-Authors: Christof Holzer, Anna Maria Wernbacher, Jan M. Senekowitsch, Karl Gatterer, Anne-marie KeltererAbstract:The energy levels within the (7)F and (5)D manifolds of trivalent europium were computed for the Free Ion and in the crystal field of 6-9 water molecules. Fully relativistic Kramers pairs configuratIon interactIon (KRCI) calculatIons were performed with different correlatIon spaces for the Free Ion, and with the complete open-shell configuratIon interactIon (COSCI) method including the 4f electrons in the active space for the water clusters. The best agreement with experimental data was found with the KRCI method or when including the spin-other-orbit effect in the COSCI calculatIons. For the Free Ion, the (7)F6 multiplet is found only 162 cm(-1) higher compared to experiment, while the (5)D(0-3) multiplets are approximately 3100 cm(-1) too high. In the crystal field of six water molecules, the multiplets with J > 0 split by 48-123 cm(-1). The energy separatIon (7)F0-(5)D0 of the unsplit multiplets is computed within 255 cm(-1)/247 cm(-1) compared to the experimental data for the Free Ion/in water. It has been found that the effect of higher coordinatIon number or lower symmetry is small, increasing the transitIon energies by only about 40 cm(-1) by lowering the (7)F(J) states by the same amount. The hypersensitive transitIon (5)D0-(7)F2 is computed at 17079 cm(-1) with the KRCI method as compared to the experimental value of 16267 cm(-1).
Jinwei Zhou - One of the best experts on this subject based on the ideXlab platform.
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Solvent-Separated Radical Ion Pairs and Free Ion Yields. 1. Effect of Temperature on Free Ion FormatIon in SolutIon
The Journal of Physical Chemistry A, 2004Co-Authors: Cheng Zhong, Jinwei Zhou, Charles L. BraunAbstract:Free Ion yields from geminate Ion pairs formed after photoinduced electron transfer are measured by the transient photocurrent method in three moderately polar solvents. Photoexcited 9,10-dicyanoanthracene (DCA) is used as the electron acceptor and alkyl-substituted benzenes as donors. It was found that, generally, there is no significant change in Free Ion yield as the temperature is increased. On the basis of a theoretical model developed under Collins−Kimball boundary conditIons, several factors are analyzed, including dielectric constants and viscosities of solvents, initial separatIon distance distributIon of geminate Ion pairs, and temperature-induced changes in recombinatIon rates. By comparing escape probabilities of geminate Ion pairs calculated at different initial formatIon and recombinatIon/separatIon distances with measured Free Ion yields, we show that Free Ions are mainly produced from the solvent-separated Ion pairs that are initially formed after electron transfer quenching of photoexcite...
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Long distance photoinduced electron transfer in solutIons: A mechanism for producing large yields of Free Ions by electron transfer quenching
The Journal of Physical Chemistry A, 2002Co-Authors: Jinwei Zhou, Roshan P. Shah, Bret R. Findley, Charles L. BraunAbstract:Free Ion and fluorescence quantum yields from the geminate Ion pairs formed by electron-transfer quenching of the excited acceptor 9,10-dicyanoanthracene by aromatic electron-donors are measured in different solvents. Theeffects of solvent polarity, energetic driving force, and steric substitutIon on Free Ion yields are studied. From the comparison of the effect of driving force on Free Ion yields and fluorescence quantum yields in different solvents, especially those of moderate polarity, it is concluded that Free Ion yields are controlled by both recombinatIon rate constants and the separatIon distance distributIon of the initially formed geminate radical Ion pairs. In dichloromethane (DCM), the recombinatIon and Free Ion formatIon processes are directly observed by fluorescence lifetime and transient photocurrent measurements. The time-resolved results indicate that Free Ion formatIon is faster than the recombinatIon process. This means that the geminate radical Ion pairs that form Free Ions and those that are neutralized by electron-transfer recombinatIon have different histories with different separatIon distances. From studies of steric effects on Free Ion yields in different solvents, it is concluded that, in polar solvents such as acetonitrile and butyronitrile, the main effect of steric hindrance is to decrease the recombinatIon rate constant and increase the escape probability, whereas in moderately polar solvents such as tetrahydrofuran, DCM and 1,2-dichlorobenzene, the main effect of steric bulk is to change the initial separatIon distance distributIon of the geminate radical Ion pairs formed by electron-transfer quenching. As an example, we compare donors such as durene (DUR) with those of greater steric bulk like 1,2,4,5-tetra-iso-propylbenzene (TIPB), for which the driving force for electron transfer is similar. The Free radical Ion yield for TIPB is more than 40 times greater than it is for DUR in DCM. This is the first example from our work in which the infinite rate boundary conditIon for Ion recombinatIon used by Onsager is not adequate, because there is no perfect sink at the origin. The Free Ion yield data are analyzed by the theory of Hong and Noolandi under the Collins and Kimball boundary conditIon.
F B Dunning - One of the best experts on this subject based on the ideXlab platform.
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Free Ion formatIon in k np sf6 collisIons at low to intermediate n velocity dependence of the number and lifetime of the product Ions
Journal of Chemical Physics, 2003Co-Authors: L Suess, R Parthasarathy, F B DunningAbstract:The rates for Free Ion productIon through electron transfer in K(np)/SF6 collisIons are measured as a functIon of Rydberg atom velocity for low-to-intermediate values of n, together with the lifetime of the product SF6− Ions against autodetachment. The data show that postattachment interactIons between the K+–SF6− product Ion pair become increasingly important as n, and the Rydberg atom velocity, are decreased. These result in the conversIon of internal energy from the SF6− Ion into translatIonal energy of the Ion pair and in a dramatic increase in SF6− Ion lifetimes. Analysis of the data using a Monte Carlo collisIon model suggests that the energy transfer is sizable, and is more than sufficient to stabilize the product SF6− Ions against autodetachment.
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velocity dependence of Free Ion productIon in k np sf6 collisIons internal to translatIonal energy transfer
Physical Review A, 1992Co-Authors: R Popple, M A Durham, R W Marawar, B G Lindsay, K A Smith, F B DunningAbstract:The velocity dependence of the rate constant for Free-Ion productIon via the Rydberg electron-transfer reactIon K({ital np})+SF{sub 6}{r arrow}K{sup +}+SF{sub 6}{sup {minus}*} has been investigated at intermediate {ital n}. The data provide evidence of a postattachment interactIon between the product Ions in which internal energy from the SF{sub 6}{sup {minus}*} Ion is converted into translatIonal energy. A similar conclusIon is reached from measurements of the velocity and angular distributIons of the product K{sup +} Ions.
