The mechanism of the multiple-pathway and multiple-step degradation reactions of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins with H and Cl atoms is investigated using the density functional theory.The electronic structures and the minimum energy path(MEP)are calculated at the B3LYP/6-311+G(d,p)level,and energetic information(single-point)is further refined at the B3LYP/6-311++G(3df,2p)level.The main possible ring opening reaction pathways of the C–O bond breakdown include indirect cleavage ring opening reaction,hydrogen addition reaction,hydrogen addition elimination reaction,and chlorine addition elimination reaction.Ten reaction steps of the six reaction pathways are considered.Our calculations indicate that hydrogen addition reaction step TS1c is of the smallest barrier height,and indirect cleavage ring opening reaction channel has the largest barrier height and is the most endothermic.
