Simultaneous adjustment of experimentally based enthalpies of formation of CF{sub 3}X, X = nil, H, Cl, Br, I, CF{sub 3}, CN, and a probe of G3 theory
- Argonne National Lab., IL (United States). Chemistry Div.
- Lucent Technologies, Murray Hill, NJ (United States). Bell Labs.
The enthalpies of formation of the title compounds have been determined by simultaneous least-squares solution of a thermochemical network containing 28 experimental measurements extracted from the literature. The new enthalpies differ considerably from the older tabulated values and now show a high degree of internal consistency achieved through excellent agreement with newer experiments, as well as older calorimetric determinations. The fitted values are: {Delta}H{sub 1298}{degree}(CF{sub 3}) = {minus}111.3 {+-} 0.5 kcal/mol ({minus}110.6 {+-} 0.5 kcal/mol at 0 K), {Delta}H{sub 1298}{degree}(CF{sub 3}H) = {minus}165.6 {+-} 0.5 kcal/mol ({minus}163.9 {+-} 0.5 kcal/mol at 0 K) {Delta}H{sub 1298}{degree}(CF{sub 3}Cl) = {minus}169.5 {+-} 0.7 kcal/mol ({minus}168.3 {+-} 0.7 kcal/mol at 0 K), {Delta}H{sub 1298}{degree}(CF{sub 3}Br) = {minus}155.3 {+-} 0.5 kcal/mol (152.4 {+-} 0.5 kcal/mol at 0 K) {Delta}H{sub 1298}{degree}(CF{sub 3}I) = {minus}140.1 {+-} 0.5 kcal/mol ({minus}138.7 {+-} 0.5 kcal/mol at 0 K), {Delta}H{sub 1298}{degree} (C{sub 2}F{sub 6}) = {minus}321.3 {+-} 0.8 kcal/mol ({minus}319.3 {+-} 0.8 kcal/mol at 0 K), and {Delta}H{sub 1298}{degree}(CF{sub 3}CN) = {minus}118.4 {+-} 0.4 kcal/mol ({minus}117.5 {+-} 0.4 kcal/mol at 0 K). Theoretical calculations at the Gaussian-3 (G3) level of theory have been performed for a subgroup of these molecules, which were problematic at the Gaussian-2 (G2) level of theory. In comparison to G2 theory, the G3 results show a remarkable improvement in accuracy and agree with experiment within <2 kcal/mol. An isodesmic bond-separation scheme brings the calculated values even closer to the experiment. In addition, the G3 value for the ionization energy of CF{sub 3}, 9.08 eV, was found to be in good agreement with the recent experimental value of 9.05{sub 5} {+-} 0.01{sub 1} eV. Further indications that the experimental value for {Delta}H{sub f}{degree}(C{sub 2}F{sub 4}) is probably too high are also presented.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 320825
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 52 Vol. 102; ISSN 1089-5639; ISSN JPCAFH
- Country of Publication:
- United States
- Language:
- English
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