Photoionization of the valence shells of the neutral tungsten atom

TL;DR

This paper presents large-scale theoretical calculations of the photoionization cross sections for neutral tungsten's valence shells using the Dirac Coulomb R-matrix method, comparing results with experimental data and previous theories.

Contribution

It introduces comprehensive Dirac Coulomb R-matrix calculations for tungsten's valence shell photoionization, including averaging over relevant levels for realistic comparison with experiments.

Findings

Theoretical cross sections align with experimental measurements after averaging over initial states.

Resonance structures identified as key features in photoionization spectra.

Provides a foundation for future electron-impact excitation and ionization studies.

Abstract

Results from large-scale theoretical cross section calculations for the total photoionization of the 4f, 5s, 5p and 6s orbitals of the neutral tungsten atom using the Dirac Coulomb R-matrix approximation (DARC: Dirac-Atomic R-matrix codes) are presented. Comparisons are made with previous theoretical methods and prior experimental measurements. In previous experiments a time-resolved dual laser approach was employed for the photo-absorption of metal vapours and photo-absorption measurements on tungsten in a solid, using synchrotron radiation. The lowest ground state level of neutral tungsten is $\rm 5p^6 5d^4 6s^2 \; {^5}D_{\it J}$, with $\it J$=0, and requires only a single dipole matrix for photoionization. To make a meaningful comparison with existing experimental measurements, we statistically average the large-scale theoretical PI cross sections from the levels associated with the ground state $\rm 5p^6 5d^4 6s^2 \; {^5}D_{\it J}[{\it J}=0,1,2,3,4]$ levels and the $\rm 5d^56s \; ^7S_3$ excited metastable level. As the experiments have a self-evident metastable component in their ground state measurement, averaging over the initial levels allows for a more consistent and realistic comparison to be made. In the wider context, the absence of many detailed electron-impact excitation (EIE) experiments for tungsten and its multi-charged ion stages allows current photoionization measurements and theory to provide a road-map for future electron-impact excitation, ionization and di-electronic cross section calculations by identifying the dominant resonance structure and features across an energy range of hundreds of eV.