Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts

Abstract

Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni − , Pd − , and Pt − ) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bound electronic states in the atom are then compared with photoelectron images collected for isoelectronic early transition metal heterogeneous diatomic molecules, M-X − (M ¼ Ti; Zr; W; X ¼ O or C). A superposition principle connecting the spectroscopy between the atomic and molecular species is observed, wherein the electronic structure of the diatomic is observed to mimic that present in the isoelectronic atom. The molecular ions studied in this work, TiO − , ZrO − , and WC − can then be interpreted as possessing superatomic electronic structures reminiscent of the isoelectronic elements appearing on the periodic table, thereby quantifying the superatom concept.cluster anions | photoelectron imaging | superatoms | angular distributions | transition metal A lchemy, the medieval practice that endeavored to transform mundane elements into the rarer, exotic variety has found many analogies in the modern physical sciences ranging from gas-phase clusters (1) to surface science (2). Particularly intriguing was a report (2) demonstrating that a tungsten carbide surface displayed similar chemical reactivity as the noble metal platinum, an element well established in its propensity for catalytically initiating a vast array of chemical transformations. By contrast, elemental tungsten alone did not exhibit comparable reactivity patterns. In order to provide insight to these findings, we have undertaken a comparative spectroscopic investigation between anionic group 10 elements ðNi − ; Pd − ; Pt − Þ and their complementary isoelectronic early transition metal molecular counterparts M-X − (M ¼ Ti; Zr; W and X ¼ O or C). We observe photoelectron signatures and angular distributions in the acquired images that exhibit very similar aspects between the respective atom and molecule. This observation suggests a correlation between the spectroscopy of an element and the isoelectronic molecular species. As a representative example, consider the formation of the diatomic molecule TiO from the united atom perceptive of molecular orbital theory (3). If only the 6 valence electrons of O ( ½He 2s 2 2p 4 ) are to be considered, subsequent combination with the 4 valence electrons of Ti ( ½Ar 3d 2 4s 2 ) creates a molecular entity with an isoelectronic configuration commensurate with the 10 valence electrons of elemental Ni ( ½Ar 3d 8 4s 2 ). In other words, the early transition metal Ti is positioned on the periodic table 6 elements removed from Ni and the intervening periodic span is traversed by the valency of atomic O. The diatomic molecule, TiO,...

Cluster Structure and Reactions: Gaining Insights into Catalytic Processes

“…Employing the technique of velocity map imaging enabled us to quantify the electronically excited state characteristics of cluster element mimics, including their anisotropies which provide information on the symmetry of the orbitals from which the electrons are ejected. Extending these quantitative measurements to a variety of systems led us to similar findings of other promising element mimics [75,76].…”

“…Although the spectra are not quantitatively identical, the similarities of the electronic excited states as well as the anisotropy parameters (b) are evident. Evidence that this is not a mere coincidence in the Pt/WC case is apparent by comparing spectra for other isovalent pairs such as TiO -, which reveals remarkable similarity [75] to that of Ni -, and similarly, ZrO -compares well with Pd -. Examples are shown in Figs.…”

Engineering Non‐sintered, Metal‐Terminated Tungsten Carbide Nanoparticles for Catalysis

“…[14] Peppernick et al demonstrated that WC À ions exhibit isoelectronic correspondence with Pt À ions. [15] Because WC exhibits high thermal and electrochemical stability while resisting common catalyst poisons such as carbon monoxide and sulfur, [1][2][3] it has been identified as a suitable candidate to replace PGM catalysts in emerging renewable energy technologies, such as fuel cells and electrolyzers. [7][8][9][10][11][16][17][18] While there are many methods to synthesize WC nanoparticles (NPs), none of the current methods can simultaneously prevent sintering of the WC nanoparticles while also mitigating surface impurity deposition.…”

Hund’s rule in superatoms with transition metal impurities

“…Further Al 13 has a large electron affinity of 3.4 eV close to that of a Cl atom (9). These analogies have prompted the concept that selected stable clusters could mimic the electronic behavior of elemental atoms and be classified as superatoms forming a third dimension of the periodic table (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). Because the properties of clusters change with size and composition, the superatoms offer the prospect of serving as the building blocks of nanomaterials with tunable characteristics (16,18).…”