We present an experimental and theoretical study of triply charged hydrogen bromide ions formed by photoionization of the inner $3d$ shell of Br. The experimental results, obtained by detecting the $3d$ photoelectron in coincidence with the two subsequent Auger electrons, are analyzed using calculated potential energy curves of ${\mathrm{HBr}}^{3+}$. The competition between the short-range chemical binding potential and the Coulomb repulsion in the dissociative process is shown. Two different mechanisms are observed for double Auger decay: one, a direct process with simultaneous ejection of two Auger electrons to final ${\mathrm{HBr}}^{3+}$ ionic states and the other, a cascade process involving double Auger decay characterized by the autoionization of ${\mathrm{Br}}^{*+}$ ion subsequent to the ${\mathrm{HBr}}^{2+}$ fragmentation.

• Received 6 January 2011

DOI:https://doi.org/10.1103/PhysRevLett.106.103002