Investigation of the electron spin resonance spectra shown by finely divided polystyrene and selectively deuterated polystyrenes, upon exposure either to hydrogen atoms or to deuterium atoms, demonstrates that the predominant reaction is the addition of a hydrogen atom to the phenyl ring, thus producing a cyclohexadienyl-type radical. The specific rate of this reaction at room temperature is estimated to be 4×103 liters mole—1·sec—1; the specific rate at which hydrogen atoms react with the cyclohexadienyl-type radical is estimated to be 106 liters mole—1·sec—1. The rate at which iodine vapor reacts with the cyclohexadienyl radicals is probably about the same value. Qualitatively, the results produce an insight into the mechanism of the radiolysis of polystyrene. It seems evident that although the mechanism is complex, both the evolved hydrogen and the crosslinking seen in the irradiation of polystyrene occur by means of radical precursors.
We have measured the absorption spectrum of the blue solid obtained in the thermal decomposition of UN's as well as those of &, RS (where R represents various organic radicals and (NHjNH),. Films were deposited in a plane aluminized quartz surface kept at liquid nitrogen temperatures and the percentage of absorbed monochromatic light over the range 20,000 to 3000 Á. was measured. The measurements are only semi-quantitative because we were not successful in preventing considerable scattering of the light by the film.
The yields and isotopic composition of hydrogen gas and the yields of bibenzyl from the 6OCO gamma radiolysis of liquid toluene, toluene-a,a,a-da in the temperature range _90° to +100°C are reported. A thermal-spike model of the radiolysis of organic liquids is presented. This model accounts for the observed low-tempe~ature depend~nce of hydrogen yields and is consistent with the estahlished chemistry of hydrogen atoms. Thls model reqUlres local "temperatures" in the thermal spike to be in the order of 500°C above the ambient temperature and suggests that a majority of the hydrogen atoms which react to form the product hydrogen gas do so in these regions of high "temperature."
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