Sentence:  It would appear that it should be possible to determine unique mechanisms for the thermal and photochemical reactions in both the liquid and <WSD>gas</WSD> 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:  the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container