Knowledge Bank

Anharmonic Structures of $n\upsilon 3$ overtones of spherical tops lie between two extreme categories. In the ""polar"" limit the major second-order perturbation is the vibrational annular momentum, $\sim \ell 23$, so the dominant splitting is proportional to $\ell 3(\ell 3+1)$. $SIF41$ seems to exhibit this behavior. In the ""Carteslan"" or ""local-mode"" limit a different anharmonic term dominates, producing extraordinary patterns of degeneracies and splitting ratios. Force-field models for hexafluorldes with a central atom whose mass is at least as great as that of Mo $(A\ge 100)$ appear to fall near this extreme. $\mathrm{<mrow\; data-mjx-texclass="ORD">32</mrow>}SF6$ is an intermediate case. Properties of the vibrational levels in the limits will be discussed, and illustrations of $n\upsilon 3$ ladders will be compared.