Ab initio study of the energetics and thermodynamics of hydrogen abstraction from fluoromethanes by O(P-3). II: CFnH4-n+O(P-3)-> CFnH4-n...O ->centerdot CFnH3-n+center dot OH (n = 0, 1, 2)

Hydrogen abstractions by O(P-3) from a set of fluorinated methanes, CFnH4-n +O(P-3) --> CFnH4-n... O --> .CFnH3-n + .OH (n = 0,1,2), were studied using ab initio methods. Geometries of the reactants and transition states were optimized at the UMP2/6-311G** level of theory, and activation energies wer e calculated using a modified GAUSSIAN 2 ((G) over cap (2)) theory. The pot ential-energy curves for the transition states were computed in order to ob tain the transmission coefficients, kappa, for the reactions studied. We fo und that kappa (aver) = 1.12 +/- 0.01. Activation energies, activation enth alpies and rate constants were computed. Good agreement, (the average diffe rence is 0.9 +/- 0.4 kcal/mol for the present study), was found between the ab initio activation energies, DeltaG(theor.)double dagger, and the experi mental activation energies, DeltaG(expt'l)double dagger. (C) 2001 Published by Elsevier Science B.V.