Photoelectron spectroscopy and theoretical study of M(IO3)2− (M = H, Li, Na, K): Structural evolution, optical isomers, and hyperhalogen behavior

Superhalogen Anions Supported by the Systems Comprising Alternately Aligned Boron and Nitrogen Central Atoms

Using DFT/(B3LYP/wB97XD/B2PLYPD) and OVGF electronic structure methods with flexible atomic orbital basis sets, we examined the series of polynuclear superhalogen anions matching the (BF₃(BN) _n F_4n+1)^- formula (for n = 1-10,13,18-20) containing alternately aligned boron and nitrogen central atoms decorated with fluorine ligands. It was found that the equilibrium structures of these anions correspond to fully extended chains (with each B and N central atom surrounded by four substituents arranged in a tetrahedral manner) and thus mimic the globally stable fully extended (all-trans) conformations of higher n-alkanes. The vertical electron detachment energies of the (BF₃(BN) _n F_4n+1)^- anions were found to exceed 8 eV in all cases and gradually increase with the increasing number of n. The approximate limiting value of vertical electron binding energy that could be achieved for such polynuclear superhalogen anions was estimated as equal to ca. 10.7 eV.

Superhalogens Among 3d-Metal Compounds: MF4, MF6, MF12, and MF18 (M = Sc-Zn)

The ground states of the neutral and anionic tetrafluoride and hexafluoride series of 3d-metal atoms from Sc to Zn were assigned by using a double-check approach in which the pure and hybrid density functional methods were interchangeably used. It was confirmed that all these neutral fluorides are superhalogens except for TiF₄. The electron affinities of the hexafluorides were shown to be consistently higher than those of the tetrafluorides in accordance with the superhalogen conception of the extra electron delocalization over a larger number of the electronegative ligands. In the search for mononuclear fluorides possessing higher electron affinities, we considered the M(F₂)₆^- and M(F₃)₆^- series where M = Sc-Zn. We found that the optimized geometrical structures in both series may be described as MF₆^-- k(F₂), k = 3 and 6, of which the geometry of the MF₆^- core mimics that of the corresponding hexafluoride anion and the F₂ dimers are kept in a bound state by polarizing forces. In these cases, the electron affinity is decreased by tenths of eV with respect to the electron affinity of the core hexafluorides due to a confinement of the extra electron by the F₂ environment.

Designing stable closo-B12 dianions in silico for Li- and Mg-ion battery applications

The electronic structures and key factors controlling the stability of [B12(ECX)12]2− were revealed. Their good stability and weak binding property towards Li+ and Mg2+ suggest their potential application in Li- and Mg-ion batteries.

Molecular Specificity and Proton Transfer Mechanisms in Aerosol Prenucleation Clusters Relevant to New Particle Formation

Atmospheric aerosol particles influence the Earth's radiative energy balance and cloud properties, thus impacting the air quality, human health, and Earth's climate change. Because of the important scientific and overarching practical implications of aerosols, the past two decades have seen extensive research efforts, with emphasis on the chemical compositions and underlying mechanisms of aerosol formation. It has been recognized that new particle formation (NPF) contributes up to 50% of atmospheric aerosols. Nowadays, the general consensus is that NPF proceeds via two distinct stages: the nucleation from gaseous precursors to form critical nuclei of sub-1-2 nm size, and the subsequent growth into large particles. However, a fundamental understanding of both the NPF process and molecular-level characterization of the critical size aerosol clusters is still largely missing, hampering the efforts in developing reliable and predictive aerosol nucleation and climate models.Both field measurements and laboratory experiments have gathered convincing evidence about the importance of volatile organic compounds (VOCs) in enhancing the nucleation and growth of aerosol particles. Numerous and abundant small clusters composed of sulfuric acid or bisulfate ion and organic molecules have been shown to exist in ∼2 nm sized aerosol particles. In particular, kinetic studies indicated the formation of clusters with one H₂SO₄ and one or two organics being the rate-limiting step.This Account discusses our effort in developing an integrated approach, which involves the laboratory cluster synthesis via electrospray ionization, size and composition analysis via mass spectrometry, photoelectron spectroscopic characterization, and quantum mechanics based theoretical modeling, to investigate the structures, energetics, and thermodynamics of the aerosol prenucleation clusters relevant to NPF. We have been focusing on the clusters formed between H₂SO₄ or HSO₄^- and the organics from oxidation of both biogenic and anthropogenic emissions. We illustrated the significant thermodynamic advantage by involving organic acids in the formation and growth of aerosol clusters. We revealed that the functional groups in the organics play critical roles in promoting NPF process. The enhanced roles were quantified explicitly for specific functional groups, establishing a Molecular Scale that ranks highly hierarchic intermolecular interactions critical to aerosol formation. The different cluster formation pathways, probably mimicking the various polluted industrial environments, that involve cis-pinonic and cis-pinic acids were unveiled as well. Furthermore, one intriguing fundamental phenomenon on the unusual protonation pattern, which violates the gas-phase acidity (proton affinity) prediction, was discovered to be common in sulfuric acid-organic clusters. The mechanism underlying the phenomenon has been rationalized by employing the temperature-dependent experiments of sulfuric acid-formate/halide model clusters, which could explain the high stability of the sulfuric acid containing aerosol clusters. Our work provides critical molecular-level information to shed light on the initial steps of nucleation of common atmospheric precursors and benchmarks critical data for large-scale theoretical modeling to further address problems of environmental interest.

Spectroscopic Signature of Proton Location in Proton Bound HSO4-·H+·X- (X = F, Cl, Br, and I) Clusters

Proton transfer plays a vital role in a variety of chemical and biological processes. The proton location in proton bound clusters, specifically, in the anions of HSO₄^-·H⁺·X^- (X = F, Cl, Br, and I), has been studied by negative ion photoelectron spectroscopy and ab initio theoretical calculations. The measured photoelectron spectra of HSO₄^-·H⁺·X^- (X = Cl, Br, and I) closely resemble those of X^- by simply shifting to higher electron binding energies, suggesting that X^- is the chromophore of the electron photodetachment, a fact clearly violating gas-phase acidity predictions. However, in the X = F case, the spectrum of HSO₄^-·H⁺·F^- is more similar to that of HSO₄^-, indicating that H⁺ stays with F^- and that the HSO₄^- moiety carries the extra electron. Accompanying theoretical analyses are in excellent agreement with the experimental measurements and observations. This work provides direct spectroscopic evidence of the proton locations, clearly showing cases in which proton affinities of the constituent bases cannot correctly predict the right chemistry involving proton transfer processes.

Noble gas insertion compounds of hydrogenated and lithiated hyperhalogens

Based on density functional theory (DFT) calculations, hydrogenated hyperhalogen HM(BO2)2, lithiated hyperhalogen LiM(BO2)2 (M = Cu, Ag, Au), and their compounds with xenon were studied. Different insertion sites of Xe resulted in various isomers. According to the natural population analysis, the Xe atom donated 0.12-0.77 electrons to HM(BO2)2 and 0.14-0.41 electrons to LiM(BO2)2 when they combined, leading to metastable charge-transfer compounds in most cases. The nature of bonding between xenon and HM(BO2)2/LiM(BO2)2 was found to be related to its location. Covalent bonds were formed when Xe bound with hydrogen atoms, as indicated by the large Wiberg bond indices of the Xe-H bonds. The same was true for most Xe-M bondings. When an Xe-O connection was formed, it was either an ionic or van der Waals force in nature depending on the specific structural feature of the isomer. A parallel study on hyperhalogen-supported Ar and Kr compounds indicated that they were not very stable and were less likely to exist at room temperature, which was in accordance with the high inertness of both Ar and Kr atoms.

Negative ion photoelectron spectra of ISO3-, IS2O3-, and IS2O4- intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

Three short-lived, anionic intermediates, ISO₃^-, IS₂O₃^-, and IS₂O₄^-, are detected during reactions between ozone and aqueous iodine/sulfur oxide microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO₃^-, IS₂O₃^-, and IS₂O₄^-, respectively. Vibrational progressions with frequencies assigned to the S-O symmetric stretching modes are discernable in the ground state transition features. Density functional theory calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by the formation of I-S and S-S bonds and can be structurally viewed as SO₃ linked with I, IS, and ISO for ISO₃^-, IS₂O₃^-, and IS₂O₄^-, respectively. The calculated ADEs and vertical detachment energies are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

Hyperhalogen properties of early-transition-metal borates

The hyperhalogen character of three series of early-transition-metal borates has been proposed.

Regioisomer-specific electron affinities and electronic structures of C70para-adducts at polar and equatorial positions with (bromo)benzyl radicals: photoelectron spectroscopy and theoretical study

Negative ion photoelectron spectroscopy shows interesting regioisomer-specific electron affinities (EAs) of 2,5- and 7,23-para-adducts of C70 [(ArCH2)2C70] (Ar = Ph, o-, m-, and p-BrC6H4). Their EA values are larger than that of C70 by 5-150 meV with the 2,5-polar adducts' EAs being higher than their corresponding 7,23-equatorial counterparts, exhibiting appreciable EA tunable ranges and regioisomeric specificity. Density functional theory (DFT) calculations reproduce both the experimental EA values and EA trends very well.