ABSTRACT
The structures and bonding properties of several lithium polysulfide clusters LiSn-/0 (n = 3-5) and Li2S4-/0 were investigated by size-selected anion photoelectron spectroscopy coupled with quantum chemistry calculations. The vertical detachment energies of LiS3-, LiS4-, and LiS5- were estimated to be 2.17 ± 0.08, 3.30 ± 0.08 and 3.66 ± 0.08 eV, respectively, and that of Li2S4- was estimated to be 3.21 ± 0.08 eV. It is found that LiS3- and LiS3 have planar quadrilateral structures, and LiS4- and LiS4 have distorted five-membered ring structures. LiS5- has a distorted six-membered ring structure while neutral LiS5 has a book-shaped structure. The lowest-lying structure of Li2S4- can be viewed as a S2 unit connecting to the Li-Li edge of a Li2S2 tetrahedron. The lowest-lying structure of neutral Li2S4 can be viewed as a S2 unit connecting to the S atoms of a Li2S2 quadrilateral. The natural population analysis (NPA) and electron localization function (ELF) analyses show that the excess electron of LiSn- is mainly localized over the sulfur chains, especially on the S atoms interacting with Li, thus, the most stable structures of LiSn- can be regarded as a Li+ cation interacting with a Sn2- dianion. The results may be useful for understanding the formation of lithium polysulfides in lithium sulfur batteries.
ABSTRACT
Bimetallic niobium-doped aluminum clusters, NbAln-/0 (n = 3-12), are investigated through a synergetic combination of size-selected anion photoelectron spectroscopy and theoretical calculations. It is found that the dominant structures of NbAln- anions with n = 3-8 can be described by gradually adding Al atoms to the NbAl3- core. Starting from n = 9, the lowest-energy geometric structures of NbAl9-12- transform into bilayer structures. In particular, NbAl12- has a C3v symmetric structure, which can be viewed as a NbAl6 regular hexagon over a bowl-shaped Al6 structure. More detailed analyses indicate that NbAl9 and NbAl12- possess unusual stability, which may be attributed to their closed-shell electron configurations with superatomic features.
ABSTRACT
Gold, although chemically inert in its bulk state, is reactive at the nanoscale and, in small clusters, even behaves like a hydrogen atom. Using a photoelectron spectroscopy experiment and first-principles theory, we show that Au also behaves like a halogen in small clusters. This is evident not only in strong resemblance between the photoelectron spectra of Au2F- and AuF2- but also in Au exhibiting one of the signature properties of halogens, its ability to form superhalogens with electron affinities higher than that of any halogen atom. For example, the electron affinity (EA) of Au2F- is 4.17 eV, while AuF2-, a known superhalogen, has an EA of 4.47 eV. Of particular interest is Au2F2, which, in spite of being a closed-shell system, is a pseudohalogen with an EA of 3.3 ± 0.1 eV. Here, one of the Au atoms behaves like a halogen, making Au2F2 mimic the property of AuF3.
