Knowledge Bank

The rotational spectrum of the stratospherically important ClONO$2$ molecule has recently been subjected to an extended analysis,}, 1-9 (2007); {\bf 244}, 113-116 (2007).} which covered four states ranging from the ground state to the $\nu 5$/$\nu 6\nu 9$ dyad at $\approx$560cm$^{-1}$.TheanalysiswasbasedonanewlyrecordedbroadbandFASSSTspectrumwithanalmostcompletecoverageofthe118-378GHzregion.\backslash vspace0.2cmTheremainingvibrationalstatesbelow560cm$^{-1}$ are the three polyads associated with successively higher excitation of the $\nu 9$ mode. These are the ($2\nu 9/\nu 7$) dyad, the ($3\nu 9/\nu 7\nu 9$) dyad, and the ($4\nu 9/\nu 72\nu 9/2\nu 7$) triad. Rotational transitions in the triad were assigned for the first time and data sets for the two dyads were considerably improved over those obtained previously.}, 8-14 (2002); {\bf 220}, 150-152 (2003).} Transition frequencies in all three polyads, for both $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$ClONO$2$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$ClONO$2$, were fitted to within experimental accuracy by using a new coupling scheme which accounted in a unified manner for the pertinent Fermi and Coriolis interactions. Various tests used to ensure that the 'true' solution has been reached are discussed.