Geminate dissociation

Figure 3. Peak photovoltage measured across a 50n resistor as a function of applied voltage and electric field, respectively. Parameter Is the relative light Intensity. The dashed curve Is the Donovan et al. (6) result In arbitrary ordinate units. The quantum efficiency (E) for geminate dissociation used to calculate lp(E)/ (E) Is taken from reference 14.

Proton transfer processes are specially important excited state properties, and several detailed time resolved studies have been reported. Time resolved fluorescence studies of excited l-naphthol-3,6-disulphonate shows there is geminate recombination by proton transfer. Another detailed study is the examination of proton transfer and solvent polarization dynamics in 3-hydroxyflavone . The dynamics of proton transfer using a geminate dissociation and recombination model has also been investigated with 8-hydroxypyrene-l,3,6-trisulphonate 5 and also with... 

A dilute I2/CCI4 solution was pumped by a 520 nm visible laser pulse, promoting the iodine molecule from its ground electronic state X to the excited states A,A, B, and ti (Fig. 4). The laser-excited I2 dissociates rapidly into an unstable intermediate (I2). The latter decomposes, and the two iodine atoms recombine either geminately (a) or nongeminately (b) ... 

Figure 3.8 STM images of the same area on Ti02(l 1 0) at 357 K (V, = 1.5 V, /, = 0.1 nA) as a function of time (At = 60s) (a) clean Ti02(l 1 0) with bridging oxygen (BBO) vacancies (b) Ti02 (1 1 0) with a geminate hydroxyl pair formed by adsorption and dissociation of a water molecule. Hv marks the...

The temperature dependence of luminescence from the sample irradiated at 1 x 1013 cm-2 with 28Si+ indicates, above —110 K, an activation energy of 90 meV for the competing nonradiative recombination process— this competing process may be the thermal dissociation of geminate pairs or bound excitons at donorlike or acceptorlike centers. The 0.09-eV value of activation energy is consistent with the results of Troxell and Watkins (1979). 

Pathway I was observed for all the 02 complexes studied, strained or unstrained, as well as for the unstrained CO-complexes. This particular pathway is the same one observed in the photodissociation of the natural heme complexes (3,4) (HbCO, MbCO, HbO and MbO ) with the exception that there is no detectable geminate recombination to the limit of our experiment, 50 ps. Pathway II, observed for the strained-CO complexes, reveals the presence of a fifth intermediate X found early in the dissociation that is either absent or undetectable in the natural or synthetic heme complexes following pathway I. The kinetics associated with the evolution of these intermediates will be discussed shortly. First, it is appropriate to examine in some detail the experimental AA difference spectra of two representative complexes, 1 -CO and 1-ET-CO. A discussion of 1-ST-CO and l-ET-O is also included for comparative purposes. ... 

Through exothermic dissociation of a neutral excited state in molecule by electron transfer to an adjacent molecule. This process leads to the generation of geminately bound electron-hole pairs as precursors of free positive and negative charges in an organic solar cell. 

Albrecht U, Bassler H (1995) Yield of geminate pair dissociation in an energetically random hopping system. Chem Phys Lett 235 389... 

Rubel O, Baranovskii SD, Stolz W, Gebhard F (2008) Exact solution for hopping dissociation of geminate electron-hole pairs in a disordered chain. Phys Rev Lett 100 196602... 

Coherent dissociation Geminate recombination Dephasing Proton transfer Electron transfer Vibrational relaxation 8arrierless reactions Bimolecular reactions Ionic reactions Solvation dynamics Friction dynamics Polarization (kerr)... 

It should be stressed that the reversible chemical reactions give us better chance to observe many-particle effects since there is no need here to monitor vanishing particle concentrations over many orders of magnitude. Indeed, the fluctuation-controlled law of the approach to the reaction equilibrium similar to (2.1.61) was observed recently experimentally [85] for the pseudo-first-order reaction A + B AB of laser-excited ROH dye molecules which dissociate in the excited state to create a geminate proton-excited anion pair. The solvated proton is attracted to the anion and recombines with it reversibly. After several dissociation-association cycles it finally diffuses to long distances and further recombination becomes unobservable. 

The photochemical dissociation of a molecule AB often leads to the formation of a pair of radicals A 4- B, e.g. as in Figure 4.33. If the reaction takes place from the lowest triplet excited state of AB, the radicals will have parallel spins and cannot recombine unless a spin flip takes place to bring them to the singlet state of the geminate radical pair. 

Studying the ESPT of hydroxy aromatic sulfonates, Huppert and co-workers [40-44] suggested an alternative model based on the geminate proton-anion recombination, governed by diffusive motion. The analysis was carried out by using Debye-Smoluchowskii-type diffusion equations. Their ESPT studies in water-methanol mixtures showed that solvent effects in the dissociation rate coefficient are equal to the effects in the dissociation equilibrium constant [45], 4-Hydroxy-1-naphthalenesulphonate in a water-propanol mixture as the solvent system has been found to behave somewhat differently than water-methanol or water-ethanol media, with a possible role of a water dimer [46,47],... 

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