Sentence:  It would appear that it should be possible to determine unique mechanisms for the thermal and <WSD>photochemical</WSD> reactions in both the liquid and gas phases and to determine values for activation energies of some of the intermediate reactions 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:  a chemical reaction produced by the action of light