Sentence:  It would appear that it should be possible to determine unique mechanisms for the thermal and photochemical reactions in both the liquid and gas phases and to determine values for activation energies of some of the intermediate reactions of atoms and <WSD>free</WSD> radicals , as well as information on the heat of dissociation of the carbon halogen bond . 
Meaning of the word marked with <WSD> tags:  an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule