Ion pair vibration

Edgell, W. F. Ions Ion Pair Org. Reat Ion pair vibrational spectra of Co(CO)4 salts 1, 153(1972)... 

FIGURE 11 Femtosecond flash photolysis of gaseous sodium iodide. As the excited ion-pair vibrates, it gradually decays (lower curve) and the resulting free atoms are detected (upper curve). 

Infrared and Raman spectroscopy have been used to study both interactions between the ions and host polymer and those between cations and anions (MacCallum and Vincent, 1989). This relies on monitoring charges in the vibrational modes of anions, namely the trifluoromethanesulphonate (CF3SOJ) and perchlorate (CIO4) anions (MacCallum and Vincent, 1989). Variation in vibrational frequency and the Raman spectral line width can provide information about the influence of the environment on the molecular ions. Changes in dipole moment arising from an ion-pair vibration are Raman inactive but strong infrared absorptions, usually in the far infrared. 

Dosimetry. Ion current measurements required for absolute dosimetry were performed with a Cary 31 ionization chamber and vibrating reed electrometer. Dry nitrogen was used as filling gas for the chamber, and a W value of 34.9 e.v./ion pair was assumed for H-3 beta rays in N2 (27). Deuterium pressures in each of the reaction mixtures were great enough to ensure that less than 1% of the H-3 beta rays reached the walls of the reaction vessel (7). 

Yakov Frenkel showed in 1926 that ideal crystals could not exist at temperatures above the absolute zero. Part of the ions leave their sites under the effect of thermaf vibrations and are accommodated in the interstitial space, leaving vacancies at the sites formerly taken up. Such point defects have been named Frenkel defects. These ideas were developed further by Walter Schottky in 1929, who pointed out that defects will also arise when individual ions or ion pairs are removed from the bulk... 

A. Infrared and Raman — vibrational energy levels Vibration-translation energy transfer, solute-solvent interaction, H -bonds, ion pairs... 

A thermal oxidation of 2,3-dimethyl-2-butene, 16, occurs in NaY when the temperature of the oxygen-loaded zeolite in raised above — 20°C [35], Similar thermally initiated oxidations were not observed for the less electron rich tram-or cix-2-butene. Remarkably, pinacolone was conclusively identified as one of the products of the reaction of 16, This ketone is not a product of the photochemical Frei oxidation (vide supra) and underscores the very different character of these two reactions and the complexity of the oxygen/16 potential energy surface, A rationale for the different behavior could lie in the different electronic states of the reactive oxygen-CT complex in the thermal and photochemical reactions. Irradiation could produce an excited triplet-state CT complex ( [16 O2] ) and/ or ion pair ( [16 02 ] ) with different accessible reaction channels than those available to a vibrationally excited ground-state triplet complex ( [16 "02]) and/... 

In summary, although the BH model predicts an inverted region for the kinetics of proton in the nonadiabatic regime, the BH model is only in qualitative accord with the data derived from the proton transfer within the benzophenone-N, A -dimethylaniline contact radical ion pairs. The failure of the model lies in its ID nature as it does not take into account the degrees of freedom for the vibrations associated with the proton-transfer mode. By incorporating these vibrations into the BH model, the LH model provides an excellent account of the parameters serving to control the kinetics of nonadiabatic proton transfer. A more rigorous test for the LH model will come when the kinetic deuterium isotope effects for benzophenone-A, A -dimethylaniline contact radical ions are examined as well as the temperature dependence of these processes are measured. 

Billing R, Rehorek D.Hennig H (1990) Photoinduced Electron Transfer in Ion Pairs. 158 151 -199 Bissell RA, de Silva AP, Gunaratne HQN, Lynch PLM, Maguire GEM, McCo, CP, Sandanayake KRAS (1993) Fluorescent PET (Photoinduced Electron Transfer) Sensors. 168 223-264 Blasse (1994) Vibrational Structure in the Luminescence Spectra of Ions in Solids. 171 1-26... 

The distance to which the ion-pair separates before the ions have vibrationally relaxed (and can then be considered as discrete well-characterised species) has been the subject of much theoretical research [315—317] (see Sect. 4). It has proved a very difficult subject to develop [318], though it does appear that the majority of the distance travelled by ejected electrons is travelled once their energy is little greater than thermal (epithermal). Typical separation distances may be 5—10 nm in... 

Bimolecular photoinduced electron transfer between an electron donor and an electron acceptor in a polar solvent may result in the formation of free ions (FI). Weller and coworkers [1] have invoked several types of intermediates for describing this process (Fig.la) exciplex or contact ion pair (CIP), loose ion pair (LIP), also called solvent separated ion pair. The knowledge of the structures of these intermediates is fundamental for understanding the details of bimolecular reactions in solution. However, up to now, no spectroscopic technique has been able to differentiate them. The UV-Vis absorption spectra of the ion pairs and the free ions are very similar [2], Furthermore, previous time resolved resonant Raman investigations [3] have shown that these species exhibit essentially the same high frequency vibrational spectrum. 

Mozumder for the neutralization of an isolated ion pair in polar media [74]. The predictions are considerably more complex for solvents with a distribution of relaxation times and barrier energies that are comparable or larger than the available thermal energy. Intramolecular vibrational effects can also be important. 

Sporer (45) gives conclusive evidence for the presence of a radical intermediate [electron paramagnetic resonance (EPR), and radical polymerization] but fails to describe the path by which the intermediate radical is converted to the cation. As possibilities he cites the crossing of the excited molecule to another, undescribed state from which it reacts, and reaction during the internal conversion step in which a molecule in the excited state converts to a molecule in a high vibrational ground state. Kinetic studies by Brown et al. (46) support the formation of ion-pair intermediates in the dark reactions. 

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