No abstract

Ab initio calculations were performed on the series of H-abstraction reactions from halomethanes of by Ñuorine atom attack. The characteristics (geometry, energy, frequencies) of reactants, transition CHCl 3~x F x states and products were determined at di †erent levels of theory from HartreeÈFock to the correlated second order level MP2 with basis sets of increasing size [6-31G(d), 6-311G(d,p) and 6-311G(2d,2p)]. MÔllerÈPlesset Conventional transition state theory and tunneling corrections were used to predict rate constants at room temperature. It is shown that only large basis sets including polarisation functions and correlated energy calculations can predict thermodynamic and kinetic parameters in good agreement with experimental data.The more reliable results are obtained if the energies and the optimised geometries are calculated at the same level or at a level where the addition of more basis functions will not change the geometries. Reactivity trends along the series of studied reactions were inspected and discussed in terms of chlorine and Ñuorine substitutions.

Kinetic studies of the reactions and were performed at room temperature in the CF 3 O 2 ] Cl CF 3 O 2 ] NO gas phase using the discharge Ñow mass spectrometric technique (DFMS). The reactions were investigated under pseudo-Ðrst-order conditions with Cl or NO in large excess with respect to the radicals. The rate CF 3 O 2 constant for the reaction was measured at 298 K and the value of (1.6 ^0.3) ] 10~11 cm3 CF 3 O 2 ] NO molecule~1 s~1 is in very good agreement with all previous values. For the reaction we obtain a CF 3 O 2 ] Cl, rate constant at 298 K of (4.2 ^0.8) ] 10~11 cm3 molecule~1 s~1 in excellent agreement with the only published value. Product analysis shows that this reaction occurs via the major reaction pathway at room temperature. In addition, an ab initio theoretical study was performed to CF 3 O 2 ] Cl ] CF 3 O ] ClO gain insights on the di †erent postulated reaction pathways. There is a signiÐcant disagreement between experimental and ab initio values recommended for the formation enthalpies of and related CF 2O, CF 3 O molecules produced in this system. Consequently, we provide self-consistent values of enthalpies based on isodesmic reactions for the reaction system using the G2, G2(MP2) and CBS-Q methods. These CF 3O 2 ] Cl values are also compared with BAC-MP4 heats of formation calculated in this work.