Theoretical studies on the photodissociation mechanism of o-chlorotoluene

The photodissociation mechanism of o-chlorotoluene on the low-lying electronic states has been investigated with the use of the CASSCF and CASPT2 techniques. Our calculations indicate that o-chlorotolubene can be excited to the first singlet state (S₁) at 266 nm, and then two possible channels would be appeared. In one channel, the system could relax from the S₁ state to the S₀ state via the S₁/S ₀ intersection point, then undergoes the intramolecular hydrogen transfer to form o-5-methylene-6-chloro-1,3-cyclohexadiene, which further dissociates into benzyl and Cl radicals. In another channel, the system could relax to the T₁ state via the S₁/T₂ and T ₂/T₁ intersection points, then directly dissociates into o-tolyl and Cl radicals. The two channels were found to proceed with probabilities of similar magnitudes, which is in good agreement with the recent experiment.