A Reexamination of the Photodissociation of CH2ClCH2Cl at 147 nm. Test for Chlorine Atom Reactions

Article abstract of DOI:10.1021/j100462a013

1,2-Dichloroethane has been photolyzed at 147 nm and ca. 23 deg C as a function of reactant pressure, the additives NO and CF4, and the conversion (It/N) which is a significant variable of the system.Also investigated was the 147-nm photolysis of a mixture of 1,2-C2H4Cl2 and C2H6 which provided unequivocal evidence for the presence of chlorine atoms in the system.The major primary process is the molecular production of ethylene (ψ_C2H4=0.67) by two Cl-atom elimination.Other observed reaction products are C2H3Cl and smaller quantities of C2H2 and CH2ClCHCl2.Approximately half of the vinyl chloride yield ψ^NO_C2H3Cl=0.16) derives from the primary molecular elimination of HCl, while the balance can be attributed to radical reactions.The reaction kinetics are interpreted in terms of competitive processes of chlorine atoms which include H abstraction from the parent, Cl addition to the product olefins, and NO-catalyzed chlorine atom recombination, with H abstraction being the dominant secondary process.The results are discussed in relation to a recent investigation of this system, and contrasted to the 147-nm photolyses of more highly substituted chlorofluoroethanes for which the "two Cl-atom" mechanism has been demonstrated previously.The extinction coefficient for 1,2-C2H4Cl2 at 147 nm (296 K) has been determined as ε=(1/PL) ln(I₀/I_t)=525 +/- 90 atm^-1 cm^-1.