Structure and thermochemistry of ClO2 radicals.

The structure of ClO2 has been calculated for the X 2A‘ ground state using unrestricted Hartree–Fock (UHF), unrestricted second-order Mo/ller–Plesset perturbation (UMP2), configuration interaction using single and double excitation (CISD), and quadratic configuration interaction (QCI) ab initio molecular orbital methods. Calculations using UMP2 and CISD wave functions predict a ClO bond length of 1.728±0.01 Å. The single-configuration based QCI in the singles and doubles space with perturbation inclusion of triple substitutions, denoted QCISD(T), yield a ClO bond length of 2.205 Å. The QCI results are consistent with results of Jensen who showed that the ClO bond length is 2.181 Å using annihilated self-consistent methods (AUMP2). The thermochemistry of ClO2 radical has been calculated using MP2 and QCI methods using an isodesmic scheme. Our scheme predicts the heat of formation for ClO2 at 0 K to be 24.6±2 kcal mol-1. [ABSTRACT FROM AUTHOR]