Photodissociation of 1,1,1-Trifluorodichloroethane at 147 nm. Evidence for Chlorine Atom Reactions

Article abstract of DOI:10.1021/j100454a008

The 147-nm photolysis of CF3CHCl2 has been investigated at 23 deg C as a function of reactant pressure and conversion (It/N), with and without nitric oxide as additive.The principal reaction product is CF2CHF, with lesser yields of CF2CFCl, CF2CHCl, and four chlorofluorobutanes.At constant CF3CHCl2 pressure the observed quantum yields of the olefins decrease with increasing It/N and there is a corresponding increase in the yields of the C4 products.The quantum yields of the olefins also decrease with increasing reactant pressure at the same values of It/N.The addition of NO completely suppresses the formation of the chlorofluorobutanes, but there is a marked increase in the olefin quantum yields.These observations are interpreted in terms of reactions of chlorine atoms which derive, primarily, from the α,α elimination of the elements of (Cl)2 in the primary process.Clorine atoms so produced abstract hydrogen from the parent and add to the product olefins, processes which are the source of haloethyl radicals in the system.Nitric oxide provides an additional and dominant channel for chlorine atom removal by way of their NO-catalyzed recombination which proceeds through CINO as an intermediate.A reaction mechanism consistent with the observations is proposed and, from the functional dependence of the olefin quantum yields on It/N, limiting values have been obtained by extrapolation.The rate constant ratio for hydrogen abstraction from CF3CHCl2 by Cl atoms to Cl addition to CF2CHF was found to be k₅/k₆ = (2.2 +/- 0.5)*E-4.The extinction coefficient for CF3CHCl2 at 147 nm (296 K) has been determined as ε = (1/PL) ln(I₀/I_t) = 590 +/- 60 atm^-1Cm^-1.