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 investig ated. Cyclohexadienyl radical with lambda(max) at 300 nm is observed as dir ect evidence for the simultaneous occurrence of a radical dissociation chan nel 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) x 10(4) s(-1). The activation barrier and enthalpy of reaction are evaluated using semi-empirical PM3MM and HF/STO-3G theories and compar ed with available experimental results. (C) 1999 Elsevier Science B.V. All rights reserved.