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 <WSD>reactions</WSD> of atoms and free radicals , as well as information on the heat of dissociation of the carbon halogen bond . 
Meaning of the word marked with <WSD> tags:  (chemistry) a process in which one or more substances are changed into others