Halon Thermochemistry: Ab Initio Calculations of the Enthalpies of Formation of Fluoromethanes.
Halon Thermochemistry: Ab Initio Calculations of the
Enthalpies of Formation of Fluoromethanes.
(957 K)
Berry, R. J.; Ehlers, C. J.; Burgess, D. R. F., Jr.;
Zachariah, M. R.; Nyden, M. R.; Schwartz, M.
Journal of Molecular Structure (Theochem), Vol. 422,
89-98, 1998.
Keywords:
halons; thermochemistry; enthalpy; heat of formation
Abstract:
The ab initio G2, G2(MP2), CBS-4 and CBS-Q quantum
mechanical protocols and the parameterized BAC-MP4
procedure were used to calculate the enthalpies of
formation of ethane and the complete sereis of
fluoroethanes. Results from all methods exhibited
significant negative deviations from experiment. With
the exception of the CBS-4 and BAC-MP4 procedures, the
negative errors in the calculated enthalpies were
observed to be linearly dependent upon the number of C-F
bonds in the molecule. Application of a bond additivity
correction (BAC) parameter derived in an earlier
investigation of fluoro- and chlorofluormethanes,
removed some although not all of the systematic
deviations. Introduction of a heavy atom interaction
parameter, representing the effect of an attached carbon
on the C-F bond error, yielded corrected enthalpies
which agree with experiment to within the reported
uncertainties. The BAC-MP4 method, which has already
been parameterized with generalized BACs, yields
calculated enthalpies which average apprximately 10 kJ
mol-1 below the experimental values of [see article] in
the fluoroethanes.
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