Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Numerical Examples and Benchmarks

<p>This manuscript is concerned with numerical illustration of the theoretical framework for computing Auger decay rates based on the Feshbach-Fano approach and the equation-of-motion coupled-cluster ansatz, augmented with core-valence separation scheme. We consider two analytical approximations to the continuum orbital describing the Auger electron: a plane wave and a Coulomb wave with an effective charge. Theoretical Auger electron spectra are presented for benchmark systems (Ne, H₂O, CH₄ and CO₂) and compared with available experimental spectra. Results of the presented benchmark tests show that the proposed computational scheme provides reliable <i>ab initio</i> preditions of the Auger spectra. The reliability, cost-efficiency, and robust computational setup of this methodology offer advantages in applications to a large variety of systems. </p>

Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Numerical Examples and Benchmarks

<p>This manuscript is concerned with numerical illustration of the theoretical framework for computing Auger decay rates based on the Feshbach-Fano approach and the equation-of-motion coupled-cluster ansatz, augmented with core-valence separation scheme. We consider two analytical approximations to the continuum orbital describing the Auger electron: a plane wave and a Coulomb wave with an effective charge. Theoretical Auger electron spectra are presented for benchmark systems (Ne, H₂O, CH₄ and CO₂) and compared with available experimental spectra. Results of the presented benchmark tests show that the proposed computational scheme provides reliable <i>ab initio</i> preditions of the Auger spectra. The reliability, cost-efficiency, and robust computational setup of this methodology offer advantages in applications to a large variety of systems. </p>

Hydration of Nucleobase as Probed by Electron Emission of Uridine-5′-Mono-Phosphate (UMP) in Aqueous Solution Induced by Nitrogen K-Shell Ionization

To identify the precise early radiation processes of DNA lesions, we measure electron kinetic energy spectra emitted from uridine-5′ monophosphate (UMP) in aqueous solution for the photoionization of the N 1s orbital electron and for the following Auger effect using a monochromatic soft X-ray synchrotron radiation at energies above the nitrogen K-shell ionization threshold. The change of photoelectron spectra for UMP in aqueous solutions at different proton concentrations (pH = 7.5 and 11.3) is ascribed to the chemical shift of the N3 nitrogen atom in uracil moiety of canonical and deprotonated forms. The lowest double ionization potentials for aqueous UMP at different pH obtained from the Auger electron spectra following the N 1s photoionization values show the electrostatic aqueous interaction of uracil moiety of canonical (neutral) and deprotonated (negatively charged) forms with hydrated water molecules.

Installation of a gas terminal stripper and a gas/foil post stripper system at the 5.5 MV Demokritos Tandem Van de Graaff accelerator

A gas stripper system has been installed inside the terminal of the Demokritos TANDEM accelerator, in addition to the existing foil stripper system, while two additional post strippers (one gas and one foil) were also installed in the beam line between the analyzing and switching magnets of the accelerator. These installations were necessary for the production of He-like ion beams used in the APAPES‡ project for the investigation of electron capture phenomena in ion-atom collisions using high resolution zero-degree Auger projectile electron spectroscopy in a dedicated experimental setup already in operation since two years. Older measurements have shown that for He-like ion beams foil stripping results in the production of a mixed-state beam (1s2, 1s2s 3S), while gas stripping in the terminal can produce an almost pure ground-state (1s2) beam. Thus, using both strippers, collision measurements will allow for the selective determination of state-selective capture contributions from either the metastable- (1s2s 3S) or the ground-state of the ion by judicious analysis of both associated projectile K-Auger electron spectra. In addition, post-stripping will allow us to obtain ion charge states whose production is not possible with only one stage of stripping.

Extrinsic and Intrinsic Contributions to Plasmon Peaks in Solids

Intrinsic and extrinsic plasmons are defined and the contribution of each determined. It is shown that quantum interference between intrinsic and extrinsic satellites in X-ray photoelectron spectroscopy (XPS) as well as in Auger electron spectra (AES) does not occur for plasmon loss peaks higher than first order. Line widths in measured reflected electron energy loss spectra (EELS) are analysed by subtracting the Shirley background. Contrary to common understanding, extrinsic and intrinsic contributions by plasmon peaks can be experimentally distinguishable by comparison of line widths.