PHOTOLYSIS OF HEXAFLUOROACETONE IN PRESENCE OF H2 D2 AND HD . KINETIC ISOTOPE EFFECTS IN REACTION OF CF3 WITH MOLECULAR HYDROGEN

The photolysis of hexafluoroacetone has been used as a source of CF 3 radicals which either react with hydrogen to produce fluoroform or recombine to form hexafluoroethane. Relative rates of these reactions approximately obey the Arrhenius expressions over the temperature range from 333° to 870°K, kH2/2k21/2=9. 3×103exp[(-10 660±140)/RT] liter1/2 mole -1/2·sec-1/2, kHD/k2 1/2=7.4×103 exp[(-10 770±150)/RT], k DH/k21/2=9.6×103exp[(-11 630±130)/RT], kD2/2k21/2 = 6.9×103 exp[(-11 660±110)/RT], Direct measurements of isotope effects were obtained by mass spectrometric analysis of the fluoroform produced during photolysis with added H2/D2 mixtures or with HD. Rate constant ratios are kH2/kD2= 1.30 exp(1050/RT), kHD/kDH=0.78 exp(860/RT). The observed isotope effects are compared with those calculated on the basis of three- and six-atom LEPS and BEBO models for the activated complex.