Theoretical study of single ionization of the oxygen atom

Abstract Understanding electron-impact ionization of oxygen is crucial because of its abundance and key role in influencing plasma dynamics in both cosmic and laboratory environments. This work examines the single ionization from energy levels of the ground configuration of atomic oxygen. The direct ionization (DI) and excitation-autoionization (EA) processes are examined for the 2 s and 2 p subshells of the ground configuration. The scaled distorted wave (sDW) cross sections, calculated using the experimental ionization threshold, show a good agreement with measurements. Additionally, the sDW results closely follow those obtained using the binary encounter Bethe model. A comparison of the DI 2 s and 2 p cross sections, previously calculated using the B-spline R-matrix-with-pseudostates (BSR) method, to the sDW data reveals similar peak values, except for the 1 S 0 level, where the BSR calculations predict ∼15% higher contribution for the DI 2 p channel relative to the sDW data. For the EA process, the sDW cross sections exceed the BSR calculations by approximately a factor of two. For spin-forbidden transitions, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mi>p</mml:mi> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mi>P</mml:mi> <mml:mo>→</mml:mo> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mn>3</mml:mn> <mml:msup> <mml:mrow> <mml:mi>s</mml:mi> <mml:mspace width="0.25em"/> </mml:mrow> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> </mml:msup> <mml:mi>S</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mi>p</mml:mi> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mi>P</mml:mi> <mml:mo>→</mml:mo> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mn>3</mml:mn> <mml:msup> <mml:mrow> <mml:mi>p</mml:mi> <mml:mspace width="0.25em"/> </mml:mrow> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> </mml:msup> <mml:mi>P</mml:mi> </mml:math> , the sDW cross sections are slightly lower than those predicted by the BSR method. These findings highlight reliability of the sDW method for oxygen ionization modeling and suggest correlation effects may explain discrepancies with BSR.