Valence and Rydberg States

Most frequently interactions between states of the same electronic symmetry are between a Rydberg state and a valence state and are often referred to in the literature as valence Rydberg mixing. In the following, a distinction is drawn between these two classes of electronic states. 

The spin-orbit multiplet splitting of Rydberg states may originate either from the outer Rydberg electron or the ion core (Acore L Score 5)- The 

Molecule Rydberg state Rydberg orbital A (atom)0 AR(obs) Valence state Ay(obs) 

Consequently, the spin-orbit constants for A 0 Rydberg states will be smaller than those of the valence states constructed from orbitals of smaller n values. In Table 5.3, spin-orbit constants of valence and Rydberg states of the same molecule are compared. 

Note that a Rydberg state is generally well described by a single electronic configuration of the form 

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In recent years, the theoretical study of ethene photochemistry has been looked at in considerable detail and has dealt with valence and Rydberg states, " substituent effects, and cycloaddition reactions." ... 

Electrostatic Perturbations Between Valence and Rydberg States.312... 

Figure 6.5 Deperturbed potential curves for the mutually interacting 2II valence and Rydberg states of NO. [Prom Gallusser and Dressier (1982).]...

The energy spacing between consecutive (n — 1/2, n + 1/2) members of a Rydberg series is 2hdft/n 3, where 3 is the Rydberg constant (109737 cm-1) and n is the (non-integer) effective principal quantum number. The intensities of transitions between valence and Rydberg states are controlled by a... 

It is, however, also clear that quantitative results can be obtained only when the basis sets are large enough to treat the different types of excited states on a comparable level of accuracy. This means that the basis set must be able to describe equally well valence and Rydberg states, and flexible enough to cover states of an ionic nature at the same time as less diffuse covalent states. 

The theoretical studies on imidazole are scarce. A recent MRCI study by Machado and Davidson [137] considered valence and Rydberg states together for the first time. On the other hand, the available experimental spectra of imidazole are limited to methanol, ethanol, and aqueous solutions and it is difficult to establish the effects of the solvent on the different transitions. The structure of the computed gas-phase spectrum differ from the spectra in a solvated medium. An unambiguous assignment of the main valence bands in the spectrum of imidazole thus requires consideration of such effects. The reaction field method, explained above, was employed with the CASSCF/CASPT2 method to analyze the influence of the solvent on the valence states of... 

Due to several reasons, including its small size, complex spectrum mixing valence and Rydberg states, relation to... 

A suitable functional should obviously also provide reliable results, namely (i) accurate ground-state geometries/vibrational frequencies, (ii) balanced description of valence and Rydberg states, (iii) balanced description of bright and dark excited states, (iv) good excited-state geometries/vibrational frequencies, and (v) a correct description of charge transfer states. 

Falden, H. H., Falster-Hansen, K. R., Bak, K. L., Rettrup, S., and Sauer, S. P. A. (2009). Benchmarking second order methods for the calculation of vertical electronic excitation energies Valence and Rydberg states in polycyclic aromatic hydrocarbons. J. Phys. Chem. A, 113, 11995-12012. 

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