Halon thermochemistry: Calculated enthalpies of formation of chlorofluoromethanes
- Wright Lab., Wright-Paterson AFB, OH (United States)
- National Inst. of Science and Technology, Gaithersburg, MD (United States)
- Sandia National Lab., Livermore, CA (United States)
- Univ. of North Texas, Denton, TX (United States)
The ab initio G2, G2(MP2), CBS-4, CBS-Q, and BAC-MP4 methods have been used to calculate the enthalpies of formation of the series of four chloromethanes and six chlorofluoromethanes [CH{sub x} F{sub y}Cl{sub 4-x-y}, x = 0-3, y = 0-3]. Calculated values of {Delta}{sub f}H{degree} using the first four ab initio methods exhibit comparatively large systematic negative errors compared with experimental values, up to -50 kJ/mol, which are nearly linearly dependent upon the number of C-F and C-Cl bonds in the molecule. It is found for the chlorofluoromethanes that the application of bond additivity corrections (BAC`s) to the ab initio enthalpies effectively removes systematic errors in the calculations and yields values that are in close agreement with experimentally derived heats. The rms deviations of the corrected calculated enthalpies from the experimental values are 2.4, 2.6, 3.4, 4.7, and 3.8 kJ/mol for the G2(MP2), G2, CBS-Q, CBS-4, and BAC-MP4 methods, respectively. These deviations are lower than the rms errors (6.9 kJ/mol) in the experimental enthalpies. Therefore, it is concluded that any of these calculational procedures, together with bond additivity corrections to remove systematic error, may profitably be used to obtain accurate enthalpies of formation in chlorofluorocarbon species. 27 refs., 2 figs., 4 tabs.
- OSTI ID:
- 249672
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 18 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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