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Abstract

Within a joint experimental and theoretical research project, double photoionization of the He-like B³⁺ 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 1s²¹S ground-state (90.9%) and 1s²s³S metastable B³⁺ ions (9.1%), two contributions to the apparent single- and double-ionization cross sections, σ_app³⁴ and σ_app³⁵, respectively, are involved in the measurements. Ratios Y(5+)/Y(4+) of double- over single-ionization yields were experimentally determined. By multiplying the measured ratios by the known cross section σ_app³⁴, the apparent cross section σ_app³⁵ for double ionization was inferred. Using the information thus obtained, the measured yield of B⁵⁺ ions produced from hydrogenlike B⁴⁺ could also be normalized. The results show good agreement with theoretical benchmark cross sections σ⁴⁵ for single photoionization of B⁴⁺. Convergent close-coupling calculations were performed to determine double-photoionization cross sections σ³⁵ for B³⁺(1s²) and B³⁺(1s2s) ions. The result for the ground state agrees very well with theoretical data obtained previously with an intermediate-energy R-matrix approach. Within the systematic uncertainty of the normalized experimental cross sections, calculated and measured data are in agreement with one another.