Sentence:  Furthermore , the exchange would not be expected to be sensitive to trace amounts of impurities because it would not be apt to be a chain reaction since the activation energy for abstraction of chlorine by a chlorine <WSD>atom</WSD> would be expected to be too high ; also it would be expected that * * f would compete very effectively with any impurities as a scavenger for * * f radicals . 
Meaning of the word marked with <WSD> tags:  (physics and chemistry) the smallest component of an element having the chemical properties of the element