Exchange interaction effects in NO core-level photoionization cross-sections

A Rüdel,J Viefhaus,A M Bradshaw,K Maier,O Kugeler,U Hergenhahn,P Lin,R R Lucchese,E E Rennie

doi:10.1088/1367-2630/7/1/189

Abstract

The effect of the exchange interaction in the photoionization continuum is investigated, using N 1s photoionization of NO into the 1s−12π (1Π) and (3Π) final states as an example. The separation in energy of these two final states is 1.41 eV. Significant differences in their partial photoionization cross-sections are observed over a wide range of energies and cannot be accounted for by the different multiplicity of the states. We suggest that the deviation of the 3Π/1Π cross-section ratio from the statistical weighting at intermediate energies is dominated by the difference in the final-state potential experienced by the photoelectron and at asymptotically high energies by the multiplet-dependent amount of intensity going into multi-electron (shake-up) processes. Calculations underpinning this point are presented. We also show supporting measurements of the 3Π/1Π cross-section ratio for O 1s ionization and the absolute photoabsorption cross-section for NO over a wide energy range covering the core level region.

Highlights

The basic features of the N 1s photoelectron spectrum of NO are known from investigations with a Mg Kα X-ray source by Bagus et al [19]
In the σ-channel of the ion yield, at the N K-edge a double structure of the resonance was observed, which was interpreted with the aid of spin-state resolved photoelectron spectra as a first maximum due to double excitations, followed by a single-shape resonance, which can decay in both the 3 and 1 channel [23]
Experimental results were obtained at several runs at the synchrotron radiation facilities NSLS (Brookhaven, USA), HASYLAB (Hamburg, Germany) and BESSY (Berlin, Germany)

Summary

Experiment

Experimental results were obtained at several runs at the synchrotron radiation facilities NSLS (Brookhaven, USA), HASYLAB (Hamburg, Germany) and BESSY (Berlin, Germany). The bulk of the photoelectron spectra were taken on the X1B undulator beamline at the NSLS [25], using a stationary, magic angle cylindrical mirror analyser (CMA), the axis of which is collinear with the incoming synchrotron radiation beam [26].A rotationally symmetric slit around the interaction region served as the gas inlet. A series of NO O 1s main line spectra was recorded with a pass energy of 15 eV and a photon energy resolution of 200–240 meV. At HASYLAB, an electron time-of-flight (TOF) analyser, similar to the one described in [29], was used under the quasi-magic angle in a plane perpendicular to the light propagation axis In this setup, the target gas entered the interaction region through a thin needle (∅ = 220 μm) mounted perpendicular to the photon beam.

Theory

Results

Discussion

Concluding remarks