Rydberg series

Such a series of lines is called a Rydberg series [26]. These lines also converge to the ionization energy of the atom or molecule, and fitting the lines to this fonuula can give a very accurate value for the ionization energy. In the case of molecules there may be resolvable vibrational and rotational stmcture on the lines as well. 

Duncan ABF 1971 Rydberg Series in Atoms and Molecules (New York Academic)... 

By extrapolating the observed oscillational frequencies for various excited states of H2 forming a part of a Rydberg series, Birge obtained for H2+ in the normal state the value... 

A few years ago, Brint et al. [62] focused on the vacuum high-resolution spectrum, pointing out a number of well-defined Rydberg series, of special importance for theoretical benchmarks. 

The physical nature of the ZEKE states has been the subject of intense experimental and theoretical investigation in the past several years. In the well-studied case of NO,14,21 we know from the 3 cm-1 red shift of the ZEKE-PFI threshold band relative to the true adiabatic ionization potential (extrapolated from highly accurate measurements of Rydberg series) that the ZEKE states have principal quantum number n 200 and lifetime of 2 (is or longer. Recent work has found ZEKE states with lifetimes as long as 20 ps.22... 

The evaluation of ionization potentials by spectroscopic methods (adiabatic IA), yields very accurate values. This amounts to identifying an appropriate Rydberg series in the absorption spectroscopy of complex atoms or molecules. The excitations leading to Rydberg-like series may be expressed as... 

Rydberg series were detected in molecular spectra in the early 1930 s, notably by W. C. Price who showed that they arose from the outer electrons. These can usually be fairly well classified in terms of the structure of the molecule, e.g. non-bonding electrons on particular atoms or electrons of double bond systems. Non-bonding electrons give more nearly atomic Rydberg series, with many numbers observable, and correspondingly accurate ionization potentials have been recorded. Most of the earlier measurements belong to this class. 

FlO. 4. Vacuum-ultra violet absorption spectrum of oxygen gas. The positions at which Rydberg series convergence limits occur are marked X—X. (We are indebted to Professor W. C. Price for this photograph.)... 

Other experimental evidence leads to essentially the same conclusion regarding the n ionization of pyridine. El Sayed and Kasha (1961) have detected Rydberg series in the absorption spectrum similar to those in benzene and ascribable to n orbitals (9-266 e.v., 02 11-56 e.v., 62) and, in addition, reported a fragmentary series leading to a third ionization potential of 10-3 e.v. which they ascribed to the nitrogen lone pair. Similar values are found by photoelectron spectroscopy which also indicated the 10-3 e.v. (10-54 e.v.) level to be only weakly bonding. 

The asymptotic -1 /r-behaviour of the KS x-only potential, which leads to a Rydberg series of excited levels even for neutral atoms, is identified as the main source of this difference. 

The 1415 A. group of bands is the first member of a Rydberg series of CH2, of which three others at shorter wavelengths were also found.63 Extrapolation to the series limit led to an ionization potential for CH2 of 10.4 e.v. It is believed that the series converges to the ground state of the CH2+ ion, and is therefore the lowest CH2 ionization potential. 

The adiabatic Iv obtained with the spectral threshold method and that of the mass spectrometer do agree within these precision limits and also with the values from the Rydberg series.1-3 7 8... 

Figure 14. Magnified central part of the Rydberg spectrum of C6D6 shown in Fig. 13. The filled circles indicate the positions for two Rydberg series converging to different core rotational states of the ion.

H. J. Neusser For a selected intermediate J K> state we observe a couple of Rydberg series for example, for J K, = li we can identify two series under minimum residual field conditions. When we apply a stationary electric field of 300 mV/cm, additional series appear that are coupled by the electric field. All series have different limits representing different rotational states of the benzene cation. At present we cannot say whether the coupling observed under minimum residual field conditions is induced by the small stray field or by field-free intramolecular coupling. 

H. J. Neusser In this regard, I should say that, up to now, the assignment of Rydberg triplet states has not been possible. In our high-resolution spectra only Rydberg series with a small quantum defect have been observed. It appears to be questionable whether triplet series become visible through spin-orbit coupling, which is expected to be small in a molecule like benzene. 

E. W. Schlag It simply means that the electron is the slowest particle compared to the more rapid nuclear motions. For this reason, each rotation has its own Rydberg series. This is referred to typically as an inverse BO representation, similar to a Hund s case d. 

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