Aqueous solutions of perchloric acid were irradiated at 77deg;K with Cohyphen;60ggr;rays and then examined by ESR spectroscopy. The H atoms formed in these systems are stable at 77deg;K and decay only on warming the samples. The kinetics of the Hhyphen;atom decay were examined in detail for 0.13 mole fraction HClO4solutions over the temperature range 100ndash;130deg;K. There are two types of trapped H atoms, both of which decay with firsthyphen;order kinetics. The least stable type has a decay rate constant given bykthinsp;equals;thinsp;1.84thinsp;times;thinsp;103explpar;minus;thinsp;3.24thinsp;times;thinsp;103thinsp;sol;thinsp;RTrpar;secminus;1and the secondhyphen;type decays with a rate constant given bykthinsp;equals;thinsp;9.43thinsp;times;thinsp;1010explpar;minus;thinsp;8.02thinsp;times;thinsp;103thinsp;sol;thinsp;RTrpar;secminus;1. The firsthyphen;order decays are interpreted as resulting from a mechanism which has an activated release of H atoms from their traps as the ratehyphen;determining step. The resulting mobile or free H atoms then react rapidly with other radicals to complete the reaction. Based on this mechanism, the trapping energies for the two types of sites are 3.24 and 8.02 kcal/g atom, respectively.
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