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Title: DFT and AB initio calculations on two reactions between hydrogen atoms and the fire suppressants 2-H heptafluoropropane and CF3Br
Authors: Lee, EPF
Dyke, JM
Chow, WK 
Chau, FT
Mok, DKW 
Keywords: 2-H heptafluoropropane
Ab initio calculations
Barrier heights
Density functional calculations
Issue Date: 2007
Source: Journal of computational chemistry, 2007, v. 28, no. 9, p. 1582-1592 How to cite?
Journal: Journal of Computational Chemistry 
Abstract: Reaction enthalpies and barrier heights of the reactions CF3Br + H → CF3 + HBr {reaction (1)) and CF3CHFCF 3 + H → CF3CFCF3 + H2 (reaction (2)} have been calculated at the near state-of-the-art ab initio level, and also by employing the B3LYP, BH&HLYP, BB1K, MPW1K, MPWB1K and TPSS1KCIS functionals. In addition, the integrated molecular orbital + molecular orbital (IMOMO) method has been used to study reaction (2). The ab initio benchmark values of the reaction enthalpy (298 K) and barrier height (0 K) of reaction (2) are reported for the first time {-(0.7 ± 0.7) and 13.3 ± 0.5 kcal/mole respectively). When density functional theory (DFT) results are compared with ah initio benchmarks for both reactions (1) and (2), the MPWBIK functional is found to have the best performance of the six functionals used. The IMOMO method with the RCCSD/aug-cc-pVTZ and/or RCCSD(T)/aug-cc-pVTZ levels, as the high levels of calculation on the model system, gives reaction enthalpies and barrier heights of reaction (2), which agree with ab initio benchmark values to within 1 kcal/mole. Computed key geometrical parameters and imaginary vibrational frequencies of the transition state structures of reactions (1) and (2) obtained at different levels of calculation are compared. The magnitudes of the computed imaginary vibrational frequencies of the transition states of both reactions considered are found to be very sensitive to the levels of calculation used to obtain them. The heat of formation (298 K) of CF3CFCF 3 calculated at the near state-of-the-art level has a value of -(318 ± 3) kcal/mole.
ISSN: 0192-8651
DOI: 10.1002/jcc.20695
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