This process proceeds more easily than methane oxidation, as indicated by the C-H bond energies (H3C-H: 104 kcal mol -1 , Cl3C-H: 95.7 kcal mol -1 ). In fact, the energy difference (ΔE) for this process estimated from DFT calculations is negative (-3.3 kcal mol -1 ). However, this reaction step is energetically unfavorable for CDCl3 compared with CHCl3, because of its relatively higher bond energy. This could have resulted in a remarkable induction period. The radical intermediate CCl3 Hence, once CCl3 • is formed, it can rapidly react with both the singlet and triplet O2 to produce the peroxyl radical. CCl3OO • gives an alkoxy radical (CCl3O • ) through the desorption of O2 via a Russel-type mechanism, and the ΔE value for this process is estimated to be -4.9 kcal mol -1 . There are two possible reaction pathways for the generation of CCl3O • ; the first pathway is COCl2 formation through the regeneration of Cl • , and the second pathway is the mechanism of hydrogen abstraction from CHCl3 to form Cl3C • . Both pathways are estimated to be exothermic with ΔE values of -16.1 and -14.8 kcal mol -1 , respectively. The regenerated Cl • and CCl3 • are recycled to produce COCl2 until the radical chain is terminated. In addition, the generated CCl3OH yields COCl2 along with HCl, and the ΔE value for this step is also negative (-4.5 kcal mol -1 ). Thus, all the steps after the photochemical generation of Cl • , as shown in Scheme 3, are exothermic in nature and energetically favorable as a radical chain reaction.