Refined Theoretical Estimates of the Atomization Energies and Molecular Structures of Selected Small Oxygen Fluorides

The heats of formation at 298.15 K and structures of five small oxygen fluoride molecules have been determined with coupled cluster theory incorporating at least through quadruple excitations, Because the wave functions of several of these systems exhibit strong multi configuration character, correlation recovery beyond CCSD(T) was found to be essential for achieving accurate results. Comparison is made with multireference configuration interaction properties where appropriate. The final Delta H-f(298 K) values obtained in this study are FO ((2)Pi(3/2)) = 26.5 +/- 0.2, FOO (2A '') = 6.4 +/- 0.7, 0170 (B-2(2)) = 125.0 +/- 0.3, FOF ((1)A(1)) = 5.9 +/- 0.3, and FOOF ((1)A) = 6.4 +/- 0.7 kcal/mol. For FO, FOO, and FOF, the theoretical Delta H-f values with their accompanying error bars easily fall within the experimental error bars. In the case of OFO the heat of formation has not been determined experimentally. The best current Delta H-f for FOOF lies outside the NIST-JANAF experimental error bars (4.59 +/- 0.5 kcal/mol) despite the use of very high levels of theory and the adoption of what is believed to be a conservative estimate of the theoretical uncertainty. Good agreement with experiment was found for the structures.