Knowledge Bank

Many a-type (9GHz-39GHz) and b-type transitions (80GHz) of ClOO for $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}Cl$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl$ isotopomers are observed using Fourier transform microwave (FTMW) and FTMW-mmw (millimeter wave) double resonance spectroscopy. The rotational, centrifugal, spin rotation coupling, and hyperfine coupling constants are determined by least squares fits of the observed spectra. Highly accurate ab initio calculations at MRCI/aug-cc-pV5Z are also performed, which reproduce the experimental results well. Other sigle reference methods are turned out to be inappropriate for ClOO, because it is indispensable to take account of static and dynamic electronic correlations simultaneously. The $re$ structure is determined using the force field obtained by the ab initio calculations; $re(OO)=1.204\backslash AA,re(ClO)=2.081\backslash AA$, and $\Theta re(ClOO)=115.0\circ$. The nature of anomalous ClO bond become clear by the present experiments and ab initio calculations.