High-Resolution Photoelectron Imaging of Cryogenically Cooled BiB2- and BiB3- Bismuth-Boron Clusters.

We report a high-resolution photoelectron imaging study of cryogenically cooled BiB2- and BiB3- 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 BiB2 and BiB3 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-1, respectively, in the ground state of BiB2. Three vibrational frequencies are measured for the ground state of BiB3: 1194 cm-1 (B-B stretching), 782 cm-1 (B-B stretching), and 339 cm-1 (Bi-B stretching). Both BiB2- and BiB3- and their neutral ground states are found to have planar C2v structures in which the Bi atom bridges two B atoms. BiB2- is found to have a triplet spin state (3B2), consistent with its complicated photoelectron spectra, whereas BiB3- is a doublet (2B1) and neutral BiB3 is closed shell (1A1). Both BiB2 and BiB3 consist of peripheral localized Bi-B and B-B σ bonds and delocalized π and σ bonds.

On the electronic structure and spin-orbit coupling of BiB from photoelectron imaging of cryogenically-cooled BiB- anion.

We report a study on the electronic structure and chemical bonding of the BiB molecule using high-resolution photoelectron imaging of cryogenically cooled BiB- anion. By eliminating all the vibrational hot bands, we can resolve the complicated detachment transitions due to the open-shell nature of BiB and the strong spin-orbit coupling. The electron affinity of BiB is measured to be 2.010(1) eV. The ground state of BiB- is determined to be 2Π(3/2) with a σ2π3 valence electron configuration, while the ground state of BiB is found to be 3Σ-(0+) with a σ2π2 electron configuration. Eight low-lying spin-orbit excited states [3Σ-(1), 1Δ(2), 1Σ+(0+), 3Π(2), 3Π(1), 1Π(1)], including two forbidden transitions, [3Π(0-) and 3Π(0+)], are observed for BiB as a result of electron detachment from the σ and π orbitals of BiB-. The angular distribution information from the photoelectron imaging is found to be critical to distinguish detachment transitions from the σ or π orbital for the spectral assignment. This study provides a wealth of information about the low-lying electronic states and spin-orbit coupling of BiB, demonstrating the importance of cryogenic cooling for obtaining well-resolved photoelectron spectra for size-selected clusters produced from a laser vaporization cluster source.

Observation of an electron-precise metal boryne complex: [BiBH].

Metal-boron triple bonds are rare due to the electron deficiency of boron. This study uncovers a simple electron-precise metal boryne complex, [BiBH]-, which is produced within an ion trap through chemical reactions of the open-shell BiB- anion with H2. Photoelectron imaging is used to investigate the electronic structure and chemical bonding of the BiBH- complex. The B atom in the linear closed-shell BiBH- is found to undergo sp hybridization, forming a B-H single bond and a BiB triple bond. Photoelectron imaging reveals three detachment transitions from the BiBH- (1Σ+) anion to the neutral BiBH, including the ground state (2Π3/2) and two excited states (2Σ+ and 2Π1/2). Strong vibronic coupling is observed between the 2Π3/2 and 2Σ+ states, evidenced by the appearance of bending vibrations and their unique photoelectron angular distributions. The BiBH- complex not only stands as the simplest metal boryne complex, but also serves as an ideal molecular system to investigate both spin-orbit and vibronic couplings.

Photoelectron imaging of cryogenically cooled BiO- and BiO2 - anions.

The advent of ion traps as cooling devices has revolutionized ion spectroscopy as it is now possible to efficiently cool ions vibrationally and rotationally to levels where truly high-resolution experiments are now feasible. Here, we report the first results of a new experimental apparatus that couples a cryogenic 3D Paul trap with a laser vaporization cluster source for high-resolution photoelectron imaging of cold cluster anions. We have demonstrated the ability of the new apparatus to efficiently cool BiO- and BiO2 - to minimize vibrational hot bands and allow high-resolution photoelectron images to be obtained. The electron affinities of BiO and BiO2 are measured accurately for the first time to be 1.492(1) and 3.281(1) eV, respectively. Vibrational frequencies for the ground states of BiO and BiO2, as well as those for the anions determined from temperature-dependent studies, are reported.