Molecular Rydberg states

Below the photoionisation threshold a core electron in a free molecule can be excited into empty anti-bonding molecular orbitals (m.o. s) as well as into Rydberg states. These transitions are observable as sharp features directly below the corresponding absorption edge (carbon K, oxygen K etc.). Above the... 

This picture is that described by the BO approximation. Of course, one should expect large corrections to such a model for electronic states in which loosely held electrons exist. For example, in molecular Rydberg states and in anions, where the outer valence electrons are bound by a fraction of an electron volt, the natural orbit frequencies of these electrons are not much faster (if at all) than vibrational frequencies. In such cases, significant breakdown of the BO picture is to be expected. 

A femtosecond time-resolved study of reactions following excitation of 1,3-dibro-mopropane to a (n,5p) Rydberg state uncovered a striking instance of coherent dynamics in a relatively large molecular environment, one characterized by 27 internal degrees of freedom. ... 

L. Woste Prof. Neusser, you are able to select specific rotational states at very high specific Rydberg state quantum numbers n. So your orbiting electron becomes very slow, even slower than the molecular rotation. Do you see any chance to bring both into phase, causing stroboscopic effects ... 

H. J. Neusser In reply to Prof. Woste let me mention that a situation similar to the high Rydberg states I discussed has been proposed for a dipolar bound electron in molecular anions. Here large distances of the electron and small binding energies are expected. First experimental indications were found. Ion pair states represent another interesting example. 

Another interesting example is the chaotic autoionization of molecular Rydberg states caused by the interaction of the electron with the degrees of freedom of the core. We consider the model in which the core consists of a positive Coulomb charge plus a rotating dipole that lies in the same plane of the electron orbit (m = l). The Hamiltonian reads (atomic units)... 

SEPARATION OF TIME SCALES IN THE DYNAMICS OF HIGH MOLECULAR RYDBERG STATES... 

The other source of congestion is due to the molecular core. It is most readily discussed using the inverse Bom-Oppenheimer point of view to define the zero-order quantum numbers. Here each state of the ionic core has its very own series of high Rydberg states. The physical reality of this approximation is the observation [36,43] of the long-time stable ZEKE states not just below the lowest ionization threshold but also just below the threshold of ionization processes that leave an excited ionic core. Indeed, it is for this very reason that ZEKE spectroscopy is useful for the spectroscopy of ions (or for such neutrals that are produced by ionization of negative ions... 

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