Knowledge Bank

The recent advent of laser diode techniques has clearly shown the centrifugal fine structure for spherical top molecules such as $CF4$ and $SF6.\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ It turns out chat most fine structure lines are nearly degenerate clusters” of two, three, or four lines belonging to tetrahedral or octahedral symmetry species, and this superfine” structure within clusters has been resolved using saturation absorption techniques in some of the softer” clusters for $SF_{6}. {^{2}}$ Also, clusters and cluster structures had been noticed earlier in computer eigenvalue $spectra^{3}$ A theoretical framework, based upon, observations of clustering is being $developed^{4}$ The theory allows one to understand spectral features in terms of specific vibrational, rotational, and tumbling” motions of molecules. An instructive analogy can be made between level clusters and energy bands in Wannier theory of electrons in crystals. In particular, the superfine splitting of clusters is proportional to the rate at which a molecule tunnels or tumbles between different symmetry axes of rotation. Also the theory is providing simple approximate formulas for different types of rovibrational energy levels and transitions, and so it can make numerical fitting less of a chore. Finally, the theory predicts cases in which hyperfine structure Is not nearly so fine as superfine structure. Along these lines it should be possible to use superhigh resolution spectroscopy to predict unusual effects in molecular quantum electronics and laser chemistry.