Peroxy radicals computer simulations

Percent product distribution acetone 24.5 5.1, 2-methyl-2-propanol 18.8 4.0, 2-methyl-2-hydroperoxypropane 36.7 7.5, 2-methyl-propanal 14.0 3.9, 2-methyl-propanol 4.4 1.3, tertiary butylperoxide < 1.7. The peroxy radicals involved are primary 2-methyl-1-propylperoxy, primary methylperoxy and tertiary 2-methyl-2-propylperoxy. The relatively large yield of tertiary butanol is due to the interaction between CH3OO and tertiary butylperoxy radicals. Computer simulations based on the known rate coefficients for the self-reactions of these radicals [2] gave = 3 x 10" cm molecule s for the cross combination reaction. To simulate the observed ratio of primary alcohol and aldehyde requires a rate coefficient p 3 x 10" cm molecule s for the interaction between 2-methyl-1-propylperoxy and tertiary 2-methyl-2-propyl-peroxy radicals. The oxidation mechanism is quantitatively well understood. 

The results of computer simulations can be used to estimate the degree of sensitivity required for measurement of the peroxy radicals in the troposphere. Madronich and Calvert (22) gave results of 5-day simulations for free tropospheric ( clean ) and Amazon boundary layer ( moderately polluted ) conditions (Figures 1 and 2, respectively). The solid and dotted lines show the simulations with and without reactions among the peroxy radicals... 

A computer model has been developed which can generate realistic concentration versus time profiles of the chemical species formed during photooxidation of hydrocarbon polymers using as input data a set of elementary reactions with corresponding rate constants and initial conditions. Simulation of different mechanisms for stabilization of clear, amorphous linear polyethylene as a prototype suggests that the optimum stabilizer would be a molecularly dispersed additive in very low concentration which can trap peroxy radicals and also decompose hydroperoxides. 

Figure 52 shows the spectrum of an unenriched sample that was annealed at 600°C in air and irradiated (5.5 Mrad x-irradiation) at 77 K. Based on the computer simulation, the many bumps seen to the low-field side of the derivative zero-crossing are assigned to a sequence of O ions or peroxy radicals, ROO (where R represents an unspecified radical or part of the glass structure), in at least five distinguishable chemical environments. An isochronal anneal experiment showed that radicals in different environments decayed at distinctly different rates [179] consistent with their different environments. 

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