High-Resolution Photoelectron Imaging of Cryogenically Cooled BiB and BiB Bismuth-Boron Clusters.

We report a high-resolution photoelectron imaging study of cryogenically cooled BiB and BiB clusters. Vibrational features are completely resolved for the ground-state detachment transitions, providing critical information about the structures of the anionic clusters and their corresponding neutrals. The electron affinities of BiB and BiB are accurately measured to be 2.174(1) and 2.121(1) eV, respectively. The B-B and Bi-B stretching frequencies are measured to be 1262 and 476 cm, respectively, in the ground state of BiB. Three vibrational frequencies are measured for the ground state of BiB: 1194 cm (B-B stretching), 782 cm (B-B stretching), and 339 cm (Bi-B stretching). Both BiB and BiB and their neutral ground states are found to have planar structures in which the Bi atom bridges two B atoms. BiB is found to have a triplet spin state (B), consistent with its complicated photoelectron spectra, whereas BiB is a doublet (B) and neutral BiB is closed shell (A). Both BiB and BiB consist of peripheral localized Bi-B and B-B σ bonds and delocalized π and σ bonds.