Unresolvable Rydberg lines in X-ray absorption spectra of free atoms

Abstract

The authors investigate the contribution of the unseparated Rydberg states which are usually neglected, in atomic K-edge X-ray spectra. They suppose that the core hole broadening is large, so that the global contribution of all unresolved Rydberg levels introduces an apparent threshold shift with a value nearly equal to the separation of the first unresolvable Rydberg line from the series limit. The apparent threshold has the same dependence on the photon energy as the true one. The region of unresolvable Rydberg lines can be described by means of a quasi-particle approach, by introducing a pseudo-wave vector formalism. The authors perform an analysis of Ne and Ar K-edge absorption spectra. Using the present theory, they derive a very simple procedure for the evaluation of the instrumental and the core hole broadening in X-ray spectra.

Photoionization of Ne Atoms and Ne+ Ions Near the K Edge: PrecisionSpectroscopy and Absolute Cross-sections

“…The processes investigated comprise K-vacancy production via excitations The calibration measurements allowed us to further investigate photoabsorption by neutral neon as part of the present work on Ne + ions. The latter is of interest in the context of the natural widths of K-shell vacancy states in neutral and ionized neon, which are expected to be of similar size (see, for example, Teodorescu et al 1993). Moreover, the data obtained with neutral neon provide a comparative test of the theoretical approaches used for photoabsorption by Ne + ions.…”

“…e Sodhi & Brion (1984) determined the transition energy through high-resolution electron energy loss spectrometry. f Teodorescu et al (1993) determined the transition energy by using synchrotron radiation with a calibrated monochromator and by measuring relative photoabsorption cross-sections. The calibration procedures were not specified.…”

“…The experimental data available in the literature were inferred from the analysis of spectra arising from K-vacancy levels of Ne excited by irradiation of neutral neon gas. Experimental widths inferred for the ( ) + s s p Ne 1 2 2 S 2 6 2 1 2 level are 0.23 ± 0.02 eV (Gelius 1974, this value was later corrected to 0.27 eV; Svensson et al 1976), 0.30 ± 0.04 eV (Esteva et al 1983), 0.21 eV (Teodorescu et al 1993, without an estimate of the uncertainty), and 0.25 ± 0.03 eV (Avaldi et al 1995). The present experiment yielded 0.261 ± 0.005 eV.…”

“…b Esteva et al (1983). c Teodorescu et al (1993), no estimate of the uncertainty was provided. d Avaldi et al (1995).…”

X-ray absorption in atomic Cd in the K-edge region

“…A corresponding model of the profile comprising the leading lorentzian resonance and an apparent arctangent edge, shifted downward from the proper continuum threshold by the unresolved higher Rydberg resonances (Teodorescu et al, 1993), gives the lorentzian energy at 26 715.1 eV and hence the continuum threshold at (26 720.371) eV. This is in good agreement with the accepted best theoretical value (26 720.5870.41) eV, which includes nuclear-size effects and higher-order corrections (Indelicato et al, 1998;Deslattes et al, 2003).…”