Recombination, geminate

Papanikolas J M, Gord J R, Levinger N E, Ray D, Versa V and Lineberger W C 1991 Photodissociation and geminate recombination dynamics of t in mass-seiected, (Cfjj j ciuster ions J. Phys. Chem. 90 8028-40... 

Paige M E, Russell D J and Harris C B 1986 Studies of chemical reactivity in the condensed phase. II. Vibrational relaxation of iodine in liquid xenon following geminate recombination J. Chem. Phys. 85 3699-700... 

Batista V S and Coker D F 1996 Nonadiabatic molecular dynamics simulation of photodissociation and geminate recombination of liquid xenon J. Chem. Phys. 105 4033-54... 

PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18) Geminate recombination... 

Figure 4. Low-lying electronic energy surfaces of I2. These states are labeled X, A/A B, and states. The processes a, P, and y denote vibrational cooling along the X potential, geminate recombination through the states A/A, and nongeminate recombination, respectively.

B. J. Schwartz, J. C. King, J. Z. Zhang, and C. B. Harris, Direct femtosecond measurements of single collision dominated geminate recombination times of small molecules in liquids. Chem. Phys. Lett. 203(5-6), 503-508 (1993). 

In an early attempt, Mozumder (1968) used a prescribed diffusion approach to obtain the e-ion geminate recombination kinetics in the pure solvent. At any time t, the electron distribution function was assumed to be a gaussian corresponding to free diffusion, weighted by another function of t only. The latter function was found by substituting the entire distribution function in the Smoluchowski equation, for which an analytical solution was possible. The result may be expressed by... 

This difference in the yields of the symmetrical dimers in the liquid [75%] and the gas (25%) phases (75—50 = 25%) is because of the geminate recombination in the cage of the liquid. Similar results were reported for ethane and methyl acetate isolated by thermolysis of a mixture of protio- and perdeuterioacetyl peroxide [85,86]. 

The existence of cage effect was proved in the experiments on photolysis of the optically active azo-compounds. The photodecomposition of these compounds is accompanied by racemization [3], For example, the partial (40%) photolysis of optically active 2-phenylazo-(2-phenyl)-butane in a hexadecane solution provides racemization to 26% [87]. The fraction of geminate recombination was found to be 52% (hexadecane, room temperature) ... 

Trans-isomer was found to be transformed virtually into the Z-isomer due to geminate recombination ... 

The problem of retention of asymmetry of the formed free radical in the fast geminate recombination of radicals was studied by photolysis of the optically active azo-compound PhMeCH—N=NCH2Ph [88,89]. The radical pair of two alkyl radicals was initiated by the photolysis of the azo-compound in benzene in the presence of 2-nitroso-2-methylpropane as a free radical acceptor. The yield of the radical pair combination product was found to be 28%. This product PhMeEtCCH2Ph was found to be composed of 31% 5,5 -(-)(double retention), 48% meso (one inversion), and 21% R.R(+) double inversion. These results were interpreted in terms of the competition between recombination (kc), diffusion (kD), and rotation (kml) of one of the optically active radicals with respect to another. The analysis of these data gave kxo[Pg.126]

The higher the viscosity of the solvent, the higher the amount of the parent molecules formed due to the geminate recombination of radicals. The observed rate constant of decomposition of the initiator decreases with an increase in viscosity [3,90], This was observed in the decomposition of peresters and diacetyl peroxide in various solutions. Subsequently, the fraction fT of the radical pairs recombining to the parent molecule increases with an increase in the viscosity ... 

The probability of the radical pair to escape from geminate recombination (e) depends on the rate constants according to the following equation ... 

Gemifloxacin, 21 224 Geminal dihydroperoxides, 13 455-456 Geminal silanol groups, 22 380, 381 silica surface chemistry and, 22 373 Geminate recombination, 14 620 Gemopatrilat, 5 159... 

As before, we define c as the total concentration of positively charged species, which is the same as what Stannett s group designate as [C+], the total concentration of cations which have escaped geminate recombination, so that... 

Geminate Recombination. Coulomhic forces attract the Ionisation electron back to Its geminate positive partner (reaction (1) + (2)). In water and other polar media, these forces are modified by the high dielectric constant and the possibility of solvation, giving a high probability of escape. This results In a high yield... 

In some cases, a long tail can be detected in the decay. It has been assigned to geminate recombination according to the following kinetic scheme ... 

The rate constant for recombination k 3 is time-dependent and can be approximated to t 2 at long times. The geminate recombination explains the residual fluorescence intensity of AH despite the fact that pH pK (see Section 4.5.3). In restricted media, the tail is even longer because of the higher probability of recapturing a photoejected proton by geminate recombination (see Box 4.3). 

Fig. 4.11. pH dependence of emission spectra of pyranine in very acidic media. The residual fluorescence of the acidic form at pH > 3 is due to geminate recombination. 

Geminate recombination of iron(II) porphyrin with a number of isocyanides and 1-methylimidazole has been observed by T. G. Traylor, D. Magde, D. Taube and K. Jongeward, J. Amer. Chem. Soc. 109, 5864 (1987). 

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