Theoretical studies of the structure and thermochemistry of FO2 radical: Comparison of Mo/ller–Plesset perturbation, complete-active-space self-consistent-field, and quadratic configuration interaction methods

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Abstract
The structure of FO2 has been calculated for the X 2A″ ground state using Mo/ller–Plesset (MP) perturbation, complete-active-space self-consistent-field (CASSCF), and quadratic configuration interaction (QCI) ab initio molecular orbital methods. Basis sets with polarization and diffuse functions were used. Compared with the experimental structure, bond lengths obtained with MP perturbation methods are found to be consistently too short. CASSCF calculations yield a structure which varies considerably with the size of the active space and basis set used. Calculations using the single-configuration-based QCI in the single and double-space with perturbative inclusion of triple substitutions, denoted by QCISD (T), yield structures very close to the experimental structure of FO2. The thermochemistry of FO2 radical has been calculated using the MP, QCI, and gaussian-1 (G1) methods. The QCI method using isodesmic and isogyric schemes has predicted the heat of formation for FO2 at 0 K to be 8.9±3 kcal mol−1.

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