CORE-NONPENETRATING RYDBERG STATES: SPECTROSCOPIC BLACK HOLES

At first glance the exchange of energy and angular momentum between a particle as light as an electron and a system as heavy as a molecular cation seems improbable and inefficient. Molecular Rydberg spectra can reveal the nature and strength of the $e^{-}$/Ion coupling mechanisms. Our studies of the alkaline earth monohalides (CaF, CaCl, BaP), examples of uniquely simple $e^{-}/MX^{+}$ system consisting of two closed shell ions $(M^{2+}$ and $X^{-}$) where $MX^{+}$ has enormous and easily calculable multipole moments, have revealed the outline of a simple picture of the $e^{-}/MX^{+}$ interaction mechanisms. There are two types of Rydberg series, \\textbf{core-non penetrating} (near-integer effective principal quantum number $n^{*}$,negligible {l}-mixing, rapid {l}-uncoupling, unusual sensitivity to isotopic substitution or vibrational excitation through dependence of the multipole moments on the $M^{2+}$ to center-of-mass distance) and {core-penetrating} (severe {l}-mixing among all of the penetrating-{l}-values as manifest in $s\\sim p\\sim d \\sim f$ supercomplexes, slow and incomplete {l}-uncoupling, and $n^{+-}$ scaling of fine structure $parameters^{1}$). The structure and dynamics of non penetrating series are well described by a long-range multipole $model^{2,3}$. Each penetrating series may be viewed as built on an $n^{3/2}$ scaled replica of a valence $state^{1}$, where the valence state is well described by ligand field $theory^{4}$. The picture is completed by outside the core dipole and quadrupole interactions between penetrating and non penetrating $series^{5}$. Although by revealing the values of the ion-core multipole moments and polarizabilities, the non penetrating series should pay a central role in describing the $e^{-}$/ion interaction, these series have been surprisingly resistant to direct, systematic exploration.