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Reaction:   SF₆ + Al → SF₅ + AlF
Reaction order:   2
Temperature:   500 - 800 K
Rate expression:   2.2x10^-10 [cm³/molecule s] e^{-45187 [J/mole]/RT}
Category:  Theory
Data type:   Ab initio
Comments:   Rate expression given is based on MP2/6-311++G(2d) energies (and geometries).

In this work, ab initio and DFT calculations were also used to compute transition states and heats of reactions. MP2, BH&HLYP, and B3LYP theories were used with 6-31G(D), 6-311++G(2d), aug-cc-pVTZ basis sets. No transition state could be found using B3LYP theory. Computed heats of reaction were found to be ?58-65) kcal/mol (exothermic) depending on level of theory compared to ?8.0(3.8) kcal/mol for experimental value or generally at least 3-5 kcal/mol high (less exothermic). Computed barriers were on the order of 10-13 kcal/mol depending on level of theory compared to experimental derived activation energy of 9.5(0.4) kcal/mol or on the order of 1-2 kcal/mol high. Computed pre-exponential factors were on the order of 1-2 E-10 cm3/molecule/s compared to 6.8(2.2) cm3/molecule/s or on the order of 3-4 times lower. Converting these into rate constants, the ab initio derived rate constants were on the order of 6-10 times lower than the experimental value. The low A factor was interpreted to mean that the computed transition states were too tight.

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Rate constant values calculated from the Arrhenius expression: