Shape resonances inK-shell photodetachment of small size-selected clusters: Experiment and theory

$K$-shell photodetachment of size-selected ${{\mathrm{B}}_{2}}^{\ensuremath{-}}$ and ${{\mathrm{B}}_{3}}^{\ensuremath{-}}$ cluster anions has been measured and calculated. The experimental absolute photodetachment cross sections exhibit bound resonances below threshold and two shape resonances above the $K$-shell threshold. Similar results were obtained for all of the cationic products observed, ${\mathrm{B}}^{+}$ and ${{\mathrm{B}}_{2}}^{+}$ from ${{\mathrm{B}}_{2}}^{\ensuremath{-}}$, as well as ${\mathrm{B}}^{+}$, ${{\mathrm{B}}_{2}}^{+}$, and ${{\mathrm{B}}_{3}}^{+}$ from ${{\mathrm{B}}_{3}}^{\ensuremath{-}}$. The overall agreement between measured and calculated photodetachment cross sections is very good. However, the theoretical study yielded additional bound resonances not observed in the experimental data.