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  1. 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. 
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  2. 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. 
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  3. Photoelectron spectroscopy combined with quantum chemistry has been a powerful approach to elucidate the structures and bonding of size-selected boron clusters (B n − ), revealing a prevalent planar world that laid the foundation for borophenes. Investigations of metal-doped boron clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The current review focuses on recent advances in transition-metal-doped boron clusters, including the discoveries of metal-boron multiple bonds and metal-doped novel aromatic boron clusters. The study of the RhB − and RhB 2 O − clusters led to the discovery of the first quadruple bond between boron and a transition-metal atom, whereas a metal-boron triple bond was found in ReB 2 O − and IrB 2 O − . The ReB 4 − cluster was shown to be the first metallaborocycle with Möbius aromaticity, and the planar ReB 6 − cluster was found to exhibit aromaticity analogous to metallabenzenes. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates. 
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  4. Borophenes are atom-thin boron layers that can be grown on coinage metal substrates and have become an important class of synthetic 2D nanomaterials. The interactions between boron and substrates are critical to understand the growth mechanisms of borophenes. Here, we report an investigation of copper-boron interactions in the Cu 2 B 8 − bimetallic cluster using photoelectron spectroscopy and quantum chemical calculations. Well-resolved photoelectron spectra are obtained at several photon energies and are combined with theoretical calculations to elucidate the structures and bonding of Cu 2 B 8 − . Global minimum searches reveal that Cu 2 B 8 − consists of a Cu 2 dimer atop a B 8 molecular wheel with a long Cu–Cu bond length close to that in Cu 2 + . Chemical bonding analyses indicate that there is clear charge transfer from Cu 2 to B 8 , and the Cu 2 B 8 − cluster can be viewed as a [Cu 2 + ]-borozene complex, [Cu 2 + ][B 8 2– ]. In the neutral cluster, no Cu–Cu bond exists and Cu 2 B 8 consists of two Cu + centers interacting with doubly aromatic B 8 2− borozene. The charge transfer interactions between Cu and boron in the Cu 2 B 8 − cluster are analogous to charge transfer from the copper substrate to the first borophene layer recently reported to be critical in the growth of bilayer borophenes on a Cu(111) substrate. 
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  5. The concept of metalla-aromaticity proposed by Thorn–Hoffmann ( Nouv. J. Chim . 1979, 3, 39) has been expanded to organometallic molecules of transition metals that have more than one independent electron-delocalized system. Lanthanides, with highly contracted 4f atomic orbitals, are rarely found in multiply aromatic systems. Here we report the discovery of a doubly aromatic triatomic lanthanide-boron molecule PrB 2 − based on a joint photoelectron spectroscopy and quantum chemical investigation. Global minimum structural searches reveal that PrB 2 − has a C 2v triangular structure with a paramagnetic triplet 3 B 2 electronic ground state, which can be viewed as featuring a trivalent Pr(III,f 2 ) and B 2 4− . Chemical bonding analyses show that this cyclo-PrB 2 − species is the smallest 4f-metalla-aromatic system exhibiting σ and π double aromaticity and multiple Pr–B bonding characters. It also sheds light on the formation of the rare B 2 4− tetraanion by the high-lying 5d orbitals of the 4f-elements, completing the isoelectronic B 2 4− , C 2 2− , N 2 , and O 2 2+ series. 
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  6. Photoelectron spectroscopy and quantum chemistry studies are used to investigate the structure and bonding of AuB 8 − . Global minimum sturctural searches show that AuB 8 − possesses a chair-like structure, which can be viewed as Au + bonded to the edge of the doubly-aromatic B 8 2− borozene, Au + [η 2 -B 8 2− ]. Chemical bonding analyses reveal that the AuB 8 − is a novel borozene complex with unique Au–borozene bonding. 
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  7. Abstract

    Lanthanide (Ln) elements are generally found in the oxidation state +II or +III, and a few examples of +IV and +V compounds have also been reported. In contrast, monovalent Ln(+I) complexes remain scarce. Here we combine photoelectron spectroscopy and theoretical calculations to study Ln-doped octa-boron clusters (LnB8, Ln = La, Pr, Tb, Tm, Yb) with the rare +I oxidation state. The global minimum of the LnB8species changes fromCstoC7vsymmetry accompanied by an oxidation-state change from +III to +I from the early to late lanthanides. All theC7v-LnB8clusters can be viewed as a monovalent Ln(I) coordinated by a η8-B82−doubly aromatic ligand. The B73−, B82−, and B9series of aromatic boron clusters are analogous to the classical aromatic hydrocarbon molecules, C5H5, C6H6, and C7H7+, respectively, with similar trends of size and charge state and they are named collectively as “borozenes”. Lanthanides with variable oxidation states and magnetic properties may be formed with different borozenes.

     
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