PAMOP: Petascale Atomic, Molecular and Optical Collision Calculations

Experimental and theoretical results are reported for single-photon single ionization of W 2+ and W 3+ tungsten ions. Experiments were performed at the photon-ion merged-beam setup of the Advanced Light Source in Berkeley. Absolute cross sections and detailed energy scans were measured over an energy range from about 20 eV to 90 eV at a bandwidth of 100 meV. Broad peak features with widths typically around 5 eV have been observed with almost no narrow resonances present in the investigated energy range. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach. The calculations were carried out for the lowest-energy terms of the investigated tungsten ions with levels 5s 2 5p 6 5d 4 5 D J J = 0, 1, 2, 3, 4 for W 2+ and 5s 2 5p 6 5d 3 4 F J J = 3/2, 5/2, 7/2, 9/2 for W 3+ . Assuming a statistically weighted distribution of ions in the initial ground-term levels there is good agreement of theory and experiment for W 3+ ions. However, for W 2+ ions at higher energies there is a factor of approximately two difference between experimental and theoretical cross sections.

Section: Theorymentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Photoionization of tungsten ions: experiment and theory for ${{\rm{W}}}^{2+}$ and ${{\rm{W}}}^{3+}$

McLaughlin

Ballance

Schippers

et al. 2016

“…An efficient parallel version [26] of the DARC [27][28][29] suite of codes was applied which has been developed [30][31][32] to address electron and photon interactions with atomic systems providing for hundreds of levels and thousands of scattering channels. These codes are presently running on a variety of parallel high performance computing architectures world wide [33,34]. Recently, DARC calculations on photoionization of trans-Fe elements were carried out for Se + , Kr + , Xe + , and Xe 7+ ions [20,31,32,35] showing suitable agreement with high resolution ALS measurements.…”

Section: Theorymentioning

confidence: 99%

Single-photon single ionization of W⁺ions: experiment and theory

Müller¹,

Schippers²,

Hellhund³

et al. 2015

Experimental and theoretical results are reported for photoionization of Ta-like (W + ) tungsten ions. Absolute cross sections were measured in the energy range 16 to 245 eV employing the photon-ion merged-beam setup at the Advanced Light Source in Berkeley. Detailed photon-energy scans at 100 meV bandwidth were performed in the 16 to 108 eV range. In addition, the cross section was scanned at 50 meV resolution in regions where fine resonance structures could be observed. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach. Photoionization cross section calculations were performed for singly ionized atomic tungsten ions in their 5s 2 5p 6 5d 4 ( 5 D)6s 6 D J , J=1/2, ground level and the associated excited metastable levels with J=3/2, 5/2, 7/2 and 9/2. Since the ion beams used in the experiments must be expected to contain long-lived excited states also from excited configurations, additional cross-section calculations were performed for the second-lowest term, 5d 5 6 S J , J=5/2, and for the 4 F term, 5d 3 6s 2 4 F J , with J = 3/2, 5/2, 7/2 and 9/2. Given the complexity of the electronic structure of W + the calculations reproduce the main features of the experimental cross section quite well.

“…The present work employs an efficient parallel version [56,57] of the Dirac Atomic R-matrix Codes (DARC) [58][59][60][61][62] developed for treating electron and photon interactions with atomic systems. This suite continues to evolve [63][64][65][66] in order to provide for ever increasing larger expansions of target and collision models for electron and photon impact with heavy atomic systems.…”

Section: Theorymentioning

confidence: 99%

Photoionisation of Ca⁺ions in the valence-energy region 20–56 eV: experiment and theory

Müller

Schippers

Phaneuf

et al. 2017

Abstract. Relative cross sections for the valence shell photoionisation (PI) of 2 S ground level and 2 D metastable Ca + ions were measured with high energy resolution by using the ion-photon merged-beams technique at the Advanced Light Source. Overview measurements were performed with a full width at half maximum bandpass of ∆E = 17 meV, covering the energy range 20 eV -56 eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of ∆E = 3.3 meV. The photon energy scale was calibrated with an uncertainty of ±5 meV. By comparison with previous absolute measurements the present experimental high-resolution data were normalised to an absolute cross-section scale and the fraction of metastable Ca + ions that were present in the parent ion beam was determined to be 18±4%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the close-coupling expansion were performed for the Ca + (3s 2 3p 6 4s 2 S 1/2 ) and Ca + (3s 2 3p 6 3d 2 D 3/2,5/2 ) levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.