CrN, CuB, and AuB: A Tale of Two Dissociation Limits

Predissociation thresholds corresponding to dissociationat groundstate separated atom limits (SALs) have been recorded in this groupfor more than 100 d- and f-blockmetal-containing molecules. The metal atom electronic degeneraciesin these molecules generate a dense manifold of electronic statesthat allow high-lying vibronic levels to couple to pathways leadingto dissociation. However, CrN, CuB, and AuB fail to dissociate attheir ground SAL. Instead, the molecules remain bound at energiesthat far surpass their bond dissociation energies (BDEs), and theirbonds break only when excited at or above an excited SAL. Sharp predissociationthresholds at excited SALs nevertheless allowed BDEs to be derived:D-0(CrN): 3.941(22) eV; D-0(CuB): 2.26(15) eV;D-0((AuB)-B-11): 3.724(3) eV. A previous measurementof D-0(AlCr) is re-evaluated as dissociating to a higherenergy limit, giving a revised value of D-0(AlCr) = 1.32(2)eV. A discussion of this physical behavior is presented.

Automated summary

This study recorded predissociation thresholds of more than 100 d- and f-block metal-containing molecules, which have electron degeneracies generating a dense manifold of electronic states allowing for coupling of high-lying vibronic levels to dissociation pathways. However, CrN, CuB, and AuB fail to dissociate at their ground state, but instead remain bound at energies surpassing their bond dissociation energies. The revised values for bond dissociation energies of these molecules at excited states are provided.