Direct evidence of a radical channel in photodissociation of 1,4-cyclohexadiene with ArF laser at 193 nm

Flash-photolysis of 1,4-cyclohexadiene with ArF laser at 193 nm is investigated. Cyclohexadienyl radical with λmax at 300 nm is observed as direct evidence for the simultaneous occurrence of a radical dissociation channel along with the concerted molecular channel to form benzene and hydrogen. The radical decays with first-order kinetics with a rate coefficient of (3.0±0.2)×104 s−1. The activation barrier and enthalpy of reaction are evaluated using semi-empirical PM3MM and HF/STO-3G theories and compared with available experimental results.