Prediction of global warming potentials through computational chemistry - Testing robustness of methodology through experimental comparisons

Kinetic estimation procedures were improved because a cancellation of errors in the original CH₂F₂ work that led to accurate kinetic estimates. Variational transition state theory was used as opposed to the original transition state theory. In the original work, the Wigner tunneling correction was used, but this tended to underestimate tunneling corrections due to the use of B3LYP/6-31g* calculations and the limitations of the model. To correct this, higher level calculations were performed at the CCSD and MP4SDQ levels for use with the small curvature tunneling approach. The lowest real vibrational mode along the reaction coordinate was a hindered rotor so this was corrected. The commonly used structural factor was more rigorously assessed with the approach of Truhlar et al. The addition of the four kinetic improvements led to more robust and accurate prediction of rate constants for a host of other chemicals, including CH₄, CH₃, CHF₃, CH₃F₃, and CH₂FCF₃. We find good agreement for all kinetic based parameters for these species compared to experimental values. Radiative forcing estimates were also in good agreement with available experimental results. A larger database of chemicals were obtained where the methodology of accurately predicting global warming potentials were completely modified from theory. This is an abstract of a paper presented at the 2006 AIChE National Meeting (San Francisco, CA 11/12-17/2006).