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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.
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We report a temperature-controlled photoelectron imaging study of SbO2–, produced from a laser vaporization source and cooled in a cryogenic 3D Paul trap. Vibrationally resolved photoelectron spectra are obtained for the ground state detachment transition, yielding the bending frequencies for both SbO2 and SbO2–. Franck-Condon simulations also allow the estimate of the vibrational temperature of the trapped SbO2– anion. A near-threshold spectrum of SbO2– at a photon energy of 3.4958 eV reveals partially resolved rotational structure for the 0-0 transition, which yields an accurate electron affinity of 3.4945 ± 0.0004 eV for SbO2. The rotational simulation also yields an estimated rotational temperature of the trapped ions.more » « less
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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 BiO 2 − to minimize vibrational hot bands and allow high-resolution photoelectron images to be obtained. The electron affinities of BiO and BiO 2 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 BiO 2 , as well as those for the anions determined from temperature-dependent studies, are reported.more » « less