Photophysical kinetic simulations

The experimental and simulation results presented here indicate that the system viscosity has an important effect on the overall rate of the photosensitization of diary liodonium salts by anthracene. These studies reveal that as the viscosity of the solvent is increased from 1 to 1000 cP, the overall rate of the photosensitization reaction decreases by an order of magnitude. This decrease in reaction rate is qualitatively explained using the Smoluchowski-Stokes-Einstein model for the rate constants of the bimolecular, diffusion-controlled elementary reactions in the numerical solution of the kinetic photophysical equations. A more quantitative fit between the experimental data and the simulation results was obtained by scaling the bimolecular rate constants by rj"07 rather than the rf1 as suggested by the Smoluchowski-Stokes-Einstein analysis. These simulation results provide a semi-empirical correlation which may be used to estimate the effective photosensitization rate constant for viscosities ranging from 1 to 1000 cP. 

Following this prescription, we have performed dynamics simulations with initial velocities pointing along 24 different directions in the g-h plane and with several initial kinetic-energy values between the maximum and the minimum. The results are presented in Figure 8-12. This figure shows the CN distance in pyrrole after 40 fs (radial coordinate) as a function of the initial direction (angular coordinate). Most of initial directions lead to a CN distance of around 1.5 A and do not result in non-cyclic structures. In these cases they correspond to photophysical... 

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