Ab initio molecular orbital studies of H + C2H4 and F + C2H4. 2. Comparison of the energetics

H. Bernhard Schlegel, Kailash C. Bhalla, William L. Hase

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Abstract

Heats of reaction and barrier heights have been computed for H + C2H4 ⇄ C2H5 and F + C2H4 → C2H4F → H + C2H3F by using Møller-Plesset perturbation theory up to fourth order with the 3-21G and 6-31G* basis sets and correcting for zero-point energy. Although energy differences and activation energies for these reactions are difficult to compute directly, reliable comparisons can be made: the CH bond dissociation energy for C2H4F is 4.1 ± 0.5 kcal/mol less than C2H5 and the exit channel barrier for C2H4F → H + C2H3F is 3.5 ± 0.5 kcal/mol larger than for C2H5. By combining these and related calculations with experimental data, the following estimates are obtained: the heat of reaction for F + C2H4 → H + C2H3F, -15 ± 2 kcal/mol; the CH bond dissociation energy for C2H4F, 31.4 ± 1 kcal/mol; and the exit channel barrier for C2H4F → C2H3F + H, 5.6 ± 0.5 kcal/mol. The implications for the dynamics of the F + C2H4 reaction are discussed.

Original languageEnglish
Pages (from-to)4883-4888
Number of pages6
JournalJournal of physical chemistry
Volume86
Issue number25
DOIs
StatePublished - 1982

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