Knowledge Bank

The rotational spectrum of $CIONO2$ has been (re-) investigated in the millimeter and submillimeter regions in the ground vibrational and first excited torsional states for both $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$Cl isotopomers. A large number of $a$- and $b$-type $R$- and $Q$-branch as well as $b$-type $P$-branch transitions have been observed. This has enabled the improvement of the spectroscopic constants and the prediction of lines in the submillimeter region. Accidental near-degeneracies of rotational levels allowed the observation of a $\Delta J=2$ transition and the precise determination of the off-diagonal quadrupole coupling constant $\chi ab$. The quartic distortion constants along with the vibrational wavenumbers and inertial defects have been used to calculate a harmonic force field. The results will be related to the molecular structure determined from an electron diffraction study and to data from related molecules such as $Cl2O$.