Ultrafast Dissociation in Core-Ionized HBr Dications

Ultrafast dissociation in a molecule with a core hole is a process in which nuclear separation proceeds so rapidly that Auger decay occurs in a fragment rather than in the intact parent molecule. Multielectron-ion coincidence spectroscopy on HBr reveals sharp atomic Auger lines resulting from dissociation of HBr2+ (Br 3d)-1(4sσ)-1, demonstrating that this core-ionized state dissociates on a time scale comparable to or shorter than the Br 3d core-hole lifetime. This strong repulsion likely arises from configuration mixing involving the 4sσ hole with 2h-1p valence-hole configurations, which generates a steeply repulsive potential. These observations constitute the evidence of ultrafast dissociation in a core-ionized state and show that a doubly charged state bearing a core hole can generate a strongly repulsive potential curve under appropriate valence-hole conditions.