Rydberg-valence interactions

The bound levels of an excited state can also couple with the continuum of a dissociative state of the same symmetry, which does not cross the bound state. This process can play an important role in molecules in which e.g., Rydberg-valence interactions cause avoided crossings between excited states. Examples are provided by OH and CH. The shape of the cross section depends on the details of the molecular structure, but it may consist of a continuous background with superposed a series of resonances (cf. Figure Ic). 

The extensive calculations of Serrano-Andres et al [31] have shown a spurious valence-Rydberg mixing in the CASSCF wave functions when valence (7t,7r )and Rydberg orbitals are optimized all together in a state average calculation it was shown that these orbitals loose their diffuse character and instead tend to provide an extra correlation to valence orbitals. To avoid such interaction, the orbitals used for the Cl treatment of the electronic spectrum were obtained by a two step procedure ... 

An example of the interaction of 3s Rydberg orbitals of a molecule whose 2s and 2p orbitals are the valence orbitals and of the evolution of these orbitals into united-atom orbitals is given below. 

Potential curves for the NO molecule have been reported by Gilmore 12 and, in an earlier study, by Vanderslice el al.56 Long-range interactions were studied by Meador57 using a valence-bond framework. Studies of certain Rydberg stales have been reported by Brion et al.58 Spectroscopic data for NO are available in the compilation of Wallace32 and the extensive studies by Miescher and co-workers.59-67... 

Ba Rydberg energy levels (—) and continua (///) obtained by adding the second valence electron to these Ba+ levels. The horizontal arrows show the possible interactions between channels associated with different ion levels. Interactions with other bound states lead to series perturbations while interactions with continua lead to autoionization. 

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