Monte Carlo modelling of radical-ion recombination in multiparticle tracks

Lozovoy, Vadim V.; Anishchik, S. V.; Medvedev, N. N.; Анисимов, О. А.; Molin, Yu. N.

doi:10.1016/0009-2614(90)85082-n

Cited by 16 publications

(3 citation statements)

References 12 publications

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“…Spin Dynamics Calculations. The recombination fluorescence kinetics in a nonpolar solvent can be expressed as where F ( t ) is the recombination rate of radical ion pairs, which is assumed to be the same for both spin-correlated and noncorrelated radical ion pairs, and θ is the fraction of pairs formed in the singlet-correlated state. , The function ρ ss ( t ) describes the population of the singlet spin state of these pairs and τ fl is the lifetime of the singlet-excited states of luminophore. In a real experiment the observed fluorescence kinetics is the convolution of (2) with the apparatus response function.…”

Section: Experimental and Computational Detailsmentioning

confidence: 99%

Degenerate Electron Exchange Reaction of n-Alkane Radical Cations in Solution

et al. 2006

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The degenerate electron exchange (DEE) reaction involving radical cations (RCs) of n-nonane, n-dodecane, and n-hexadecane in n-hexane solution was studied over the temperature range 253-313 K using the method of time-resolved magnetic field effect in recombination fluorescence of spin-correlated radical ion pairs. In the dilute solutions the rate constant of DEE was found to be 200 times slower than the diffusion limit. Using n-nonane as an example, we showed that two reasons are responsible for the low value of the RC self-exchange rate: (1) conformational variability of molecules and RCs and (2) the activation barrier of DEE reaction. The calculations of the reaction enthalpy performed by the B3LYP/6-31G(d) method indicated that electron transfer can be effective only upon collision of RC with a neutral molecule either in the all-trans conformation or in the conformation differing from the latter by rotation of the end ethyl fragment. The activation barrier of the DEE reaction was estimated using the reorganization energy of the internal degrees of freedom calculated at the B3LYP level and was found to be about 6 kcal/mol. A possible influence of the interaction between RC and a neutral molecule in an encounter complex on DEE rate constant is also discussed.

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Section: Experimental and Computational Detailsmentioning

confidence: 99%

Degenerate Electron Exchange Reaction of n-Alkane Radical Cations in Solution

et al. 2006

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“…The parameter θ governs the amplitude of the TRMF effect. 25 The values of these simulation parameters are given in the caption to Figure 7. According to the simulation, the time constant of phase relaxation (T 2 ) is independent of the magnetic field strength.…”

Section: Magnetic Field Effect On the Decay Of The Recombination Fluo...mentioning

confidence: 99%

“…Other parameters for the simulation were the time constants for phase and spin−lattice relaxation, 20,21 which can be considered as the inverse overall-relaxation rates for the radical pair involved, and the fraction θ of singlet spin-correlated radical pairs, which is determined by the probability of geminate recombination in the radiation track. The parameter θ governs the amplitude of the TRMF effect . The values of these simulation parameters are given in the caption to Figure .…”

Section: Magnetic Field Effect On the Decay Of The Recombination Fluo...mentioning

confidence: 99%

Radical Cations from Dicyclopropylidenemethane and Its Octamethyl Derivative

et al. 2005

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The radical cations of dicyclopropylidenemethane (2) and its octamethyl derivative (2-Me 8 ) are prone to rearrangements into those of (2-methylallylidene)cyclopropane (2a) and its octamethyl derivative (2a-Me 8 ), respectively, by opening one three-membered ring. In contrast to the radical cations of bicyclopropylidene (1) and its octamethyl derivative (1-Me 8 ), 2 •+ and 2-Me 8 •+ are stable to opening of the second ring, because in this case the resulting species would be a non-Kekulé hydrocarbon with a quartet ground state. Similarly to 1, octamethyl substitution in 2 promotes the tendency to rearrangement. Thus, ESR and ENDOR studies indicate that the primary radical cation 2 •+ , which is formed upon γ-irradiation of 2 in a CFCl 3 matrix at 77 K, does not rearrange up to 150 K. On the other hand, when 2-Me 8 is treated in the same way, only the rearranged radical cation 2a-Me 8 •+ can be observed and characterized by its ESR and ENDOR spectra. Nevertheless, the existence of the two "missing" species, 2a •+ and 2-Me 8 •+ , is revealed by other methods. According to UV and IR studies, X irradiation of 2 in an Ar matrix leads directly to the ring-opened radical cation 2a •+ . Moreover, magnetic field effects on the decay of fluorescence, which appears upon recombination of the radical anion of p-terphenyl with a radical cation generated from 2-Me 8 in liquid octane, strongly suggest that 2-Me 8 •+ (and not 2a-Me 8 •+ ) is formed initially. From the temperature dependence of the decay, the activation energy of the ring-opening process 2-Me 8 •+ f 2a-Me 8 •+ is estimated. The radical cations 2a •+ and 2a-Me 8 •+ are formally distonic with the spin residing in the allylic moiety and the charge accommodated on the central carbon atom of the allene π-system. The intact cyclopropylidenemethylidene moiety assumes a "bisected" conformation, thus favoring an optimal interaction with the positively charged center on the π-system.

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