Direct double ionization of the He-like <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi mathvariant="normal">B</mml:mi><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:math> ion by a single photon

Within a joint experimental and theoretical research project, double photoionization of the He-like <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mrow><a:mi mathvariant="normal">B</a:mi></a:mrow><a:mrow><a:mn>3</a:mn><a:mo>+</a:mo></a:mrow></a:msup></a:math> ion by a single photon was studied in the energy range from approximately 350 to 1160 eV. With the parent-ion beam in the experiment containing both <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mn>1</c:mn><c:msup><c:mi>s</c:mi><c:mn>2</c:mn></c:msup><c:msup><c:mspace width="0.16em"/><c:mn>1</c:mn></c:msup><c:mi>S</c:mi></c:mrow></c:math> ground-state (90.9%) and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mn>1</e:mn><e:mi>s</e:mi><e:mn>2</e:mn><e:mi>s</e:mi><e:mspace width="0.16em"/><e:mmultiscripts><e:mi>S</e:mi><e:mprescripts/><e:none/><e:mn>3</e:mn></e:mmultiscripts></e:mrow></e:math> metastable <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:msup><g:mrow><g:mi mathvariant="normal">B</g:mi></g:mrow><g:mrow><g:mn>3</g:mn><g:mo>+</g:mo></g:mrow></g:msup></g:math> ions (9.1%), two contributions to the apparent single- and double-ionization cross sections, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:msubsup><i:mi>σ</i:mi><i:mrow><i:mn>34</i:mn></i:mrow><i:mtext>app</i:mtext></i:msubsup></i:math> and <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:msubsup><j:mi>σ</j:mi><j:mrow><j:mn>35</j:mn></j:mrow><j:mtext>app</j:mtext></j:msubsup></j:math>, respectively, are involved in the measurements. Ratios <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mrow><k:mi>Y</k:mi><k:mo>(</k:mo><k:mn>5</k:mn><k:mo>+</k:mo><k:mo>)</k:mo><k:mo>/</k:mo><k:mi>Y</k:mi><k:mo>(</k:mo><k:mn>4</k:mn><k:mo>+</k:mo><k:mo>)</k:mo></k:mrow></k:math> of double- over single-ionization yields were experimentally determined. By multiplying the measured ratios by the known cross section <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:msubsup><l:mi>σ</l:mi><l:mrow><l:mn>34</l:mn></l:mrow><l:mtext>app</l:mtext></l:msubsup></l:math>, the apparent cross section <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msubsup><m:mi>σ</m:mi><m:mrow><m:mn>35</m:mn></m:mrow><m:mtext>app</m:mtext></m:msubsup></m:math> for double ionization was inferred. Using the information thus obtained, the measured yield of <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:msup><n:mrow><n:mi mathvariant="normal">B</n:mi></n:mrow><n:mrow><n:mn>5</n:mn><n:mo>+</n:mo></n:mrow></n:msup></n:math> ions produced from hydrogenlike <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:msup><p:mrow><p:mi mathvariant="normal">B</p:mi></p:mrow><p:mrow><p:mn>4</p:mn><p:mo>+</p:mo></p:mrow></p:msup></p:math> could also be normalized. The results show good agreement with theoretical benchmark cross sections <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:msub><r:mi>σ</r:mi><r:mn>45</r:mn></r:msub></r:math> for single photoionization of <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:msup><s:mrow><s:mi mathvariant="normal">B</s:mi></s:mrow><s:mrow><s:mn>4</s:mn><s:mo>+</s:mo></s:mrow></s:msup></s:math>. Convergent close-coupling calculations were performed to determine double-photoionization cross sections <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:msub><u:mi>σ</u:mi><u:mn>35</u:mn></u:msub></u:math> for <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:mrow><v:msup><v:mrow><v:mi mathvariant="normal">B</v:mi></v:mrow><v:mrow><v:mn>3</v:mn><v:mo>+</v:mo></v:mrow></v:msup><v:mrow><v:mo>(</v:mo><v:mn>1</v:mn><v:msup><v:mi>s</v:mi><v:mn>2</v:mn></v:msup><v:mo>)</v:mo></v:mrow></v:mrow></v:math> and <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mrow><x:msup><x:mrow><x:mi mathvariant="normal">B</x:mi></x:mrow><x:mrow><x:mn>3</x:mn><x:mo>+</x:mo></x:mrow></x:msup><x:mrow><x:mo>(</x:mo><x:mn>1</x:mn><x:mi>s</x:mi><x:mn>2</x:mn><x:mi>s</x:mi><x:mo>)</x:mo></x:mrow></x:mrow></x:math> ions. The result for the ground state agrees very well with theoretical data obtained previously with an intermediate-energy <z:math xmlns:z="http://www.w3.org/1998/Math/MathML"><z:mi>R</z:mi></z:math>-matrix approach. Within the systematic uncertainty of the normalized experimental cross sections, calculated and measured data are in agreement with one another.