Theoretical studies of structures and stabilities of endohedral fullerenes X0/n+ @C32 (X = H,Li, Na,K, Be,Mg, Ca,B, Al,C, Si,N, P,n = 1–3)

Based on the D₃ C₃₂ fullerene, the equilibrium geometries, electronic structures, and binding energies of the endohedral fullerenes X^0/n+@C₃₂ (X = H, Li, Na, K, Be, Mg, Ca, B, Al, C, Si, N, P, n = 1–3) have been calculated using the DFT/B3LYP/6‐31G(d) method. The results show that the C₃₂ cages are slightly enlarged due to encapsulation, and the sizes of non‐neutral molecules are smaller than the corresponding neutral ones. Cages containing Li, Na, and Ca and most of the cations, except Na⁺ and K⁺, are energetically favorable. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Magnesium-Based Clusters as Building Blocks of Electrolytes in Lithium-Ion Batteries

Superhalogens, owing to their large electron affinity (EA, exceeding those of any halogen atom), play an essential role in physical chemistry as well as new material design. They have applications in hydrogen storage and lithium-ion batteries. Owing to the unique geometries and electronic features of magnesium-based clusters, their potential to form a new class of lithium salts has been investigated here theoretically. The idea is assessed by conducting ab initio computations on Li⁺/Mg_nF_2n+1-2mO_m⁻ compounds (n=2, 3; m=0-3) and analyzing their performance as potential Li-ion battery electrolytes. The Mg₃F₇⁻ cluster, with large electron binding energy (EA of 7.93 eV), has been proven to serve as a building block for lithium salts. It is shown that, apart from high electronic stability, the new superhalogen-based electrolytes exhibit a set of desirable properties, including a large band gap, high electrolyte stability window, easy mobility of the Li⁺, and favorable insensitivity to water.     

Comparison of Hydrogen and Gold Bonding in [XHX]−, [XAuX]−, and Isoelectronic [NgHNg]+, [NgAuNg]+ (X=Halogen,Ng=Noble Gas)

Quantum chemical calculations at the MP2/aug‐cc‐pVTZ and CCSD(T)/aug‐cc‐pVTZ levels have been carried out for the title compounds. The electronic structures were analyzed with a variety of charge and energy partitioning methods. All molecules possess linear equilibrium structures with D_∞h symmetry. The total bond dissociation energies (BDEs) of the strongly bonded halogen anions [XHX]^? and [XAuX]^? decrease from [FHF]^? to [IHI]^? and from [FAuF]^? to [IAuI]^?. The BDEs of the noble gas compounds [NgHNg]⁺ and [NgAuNg]⁺ become larger for the heavier atoms. The central hydrogen and gold atoms carry partial positive charges in the cations and even in the anions, except for [IAuI]^?, in which case the gold atom has a small negative charge of ?0.03 e. The molecular electrostatic potentials reveal that the regions of the most positive or negative charges may not agree with the partial charges of the atoms, because the spatial distribution of the electronic charge needs to be considered. The bonding analysis with the QTAIM method suggests a significant covalent character for the hydrogen bonds to the noble gas atoms in [NgHNg]⁺ and to the halogen atoms in [XHX]^?. The covalent character of the bonding in the gold systems [NgAuNg]⁺ and [XAuX]^? is smaller than in the hydrogen compound. The energy decomposition analysis suggests that the lighter hydrogen systems possess dative bonds X^?→H⁺←X^? or Ng→H⁺←Ng while the heavier homologues exhibit electron sharing through two‐electron, three‐center bonds. Dative bonds X^?→Au⁺←X^? and Ng→Au⁺←Ng are also diagnosed for the lighter gold systems, but the heavier compounds possess electron‐shared bonds.     

Formation of WF−6 and its dissociative products by collisional ionization

The formation of negative ions in electron transfer reactions between hyperthermal alkali atoms (Na, K) and WF₆ has been studied in the energy range 0–30 eV c.m. Relative cross sections and translational energy thresholds for ion pair formation have been measured, from which the following electron affinities (EA) and bond dissociation energies (D) have been derived: EA(WF₆) = 3.7 eV, EA(WF₅) = 1.25 eV, D(WF₅—F) = 5.1 eV, D)WF₅—F^?) = 5.4 eV, D(WF^?₅—F) = 7.6 eV. Several ion molecule reactions are discussed which result in formation of secondary fragmentation ions and WF^?₇.     

Electronic structure and properties of isoelectronic magic clusters: Al13X (X=H,Au,Li,Na,K,Rb,Cs)

The equilibrium structure, stability, and electronic properties of the Al(13)X (X=H,Au,Li,Na,K,Rb,Cs) clusters have been studied using a combination of photoelectron spectroscopy experiment and density functional theory. All these clusters constitute 40 electron systems with 39 electrons contributed by the 13 Al atoms and 1 electron contributed by each of the X (X=H,Au,Li,Na,K,Rb,Cs) atom. A systematic study allows us to investigate whether all electrons contributed by the X atoms are alike and whether the structure, stability, and properties of all the magic clusters are similar. Furthermore, quantitative agreement between the calculated and the measured electron affinities and vertical detachment energies enable us to identify the ground state geometries of these clusters both in neutral and anionic configurations.     

Gas-phase ion-molecule bimolecular and clustering reactions in dilute solutions of acetonitrile in xenon,krypton, argon,neon and helium

Gas-phase bimolecular and clustering reactions of acetonitrile in Xe, Kr, Ar, Ne and He were studied at high chemical ionization pressures in the new coaxial ion source at Auburn. With electron energies near the ionization threshold, the mass spectra are exceedingly simple and are comprised of [CH₄CH]⁺ and clusters of [CH₄CN]⁺ with various ligands such as H₂O and CH₃CN. At higher electron energies many other peaks appear. The intensities of the new peaks depend upon the ionization potential of the charge transfer gas, the ionizing electron energy and the ion source conditions, and are due to reactions of fragment ions. Residence time distributions at electron energies above the ionization threshold (∼ 30 eV) demonstrate that two molecular structures are present in the ion beam at m/z 42, one presumably is protonated acetonitrile ([CH₃CNH]⁺) while the evidence indicates that the second species does not contain acidic hydrogens. With ionizing electron energies near threshold (∼ 10. 5 eV) only one structure is observed. Studies with electron energies near the ionization threshold under high-pressure chemical ionization conditions result in greatly simplified mass spectra and are possible only because of the coaxial geometry of the ion source.     

Electronic structure of the azide ion using the SCF Xα SW method

The electronic structure of the azide ion is investigated using the SCF Xα scattered wave method. Calculated ionization energies are compared with values determined by electron spectroscopy. Transition state calculations for π_g → π*_u, σ_u → π*_u and σ_g → π*_u single electron transitions yield excitation energies near 5.7, 11.0, and 12.0 eV respectively.     

Geometries,vibrational frequencies,and electron affinities of X2Cl (X=C,Si,Ge) clusters

Ab initio quantum chemical calculations have been performed on X₂Cl^? and X₂Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree–Fock (HF), Møller–Plesset second‐ and fourth‐order (MP2, MP4), CCSD(T) level with the 6‐311+G(d) basis set. The X₂Cl (X = C, Si, Ge) and X₂Cl^? (X = Si, Ge) take a bent shape obtained at the ground state, while C₂Cl^? has a linear structure. The impact on internal electron transfer between the X₂Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc‐pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C₂Cl, Si₂Cl, and Ge₂Cl, respectively. The calculated EAs of C₂Cl and Ge₂Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The σ− selection rule in electron attachment and autoionization of diatomic molecules

It is shown theoretically that Σ⁺ ⇐ Σ⁻ transitions in electron attachment and autionization of diatomic molecules are forbidden. For the verification of this selection rule, two experimental examples are given.     

Vibration-rotation transition probabilities in CH+ and CD+

Vibrational dipole matrix elements and radiative transition probabilities have been evaluated from electric dipole moment functions for the X¹Σ⁺ states of CH⁺ and CD⁺, which were calculated from highly correlated electronic wavefunctions. The dipole moments in ν = 0 amount to 1.679 D (CH⁺) and 1.313 D (CD⁺), respectively. In comparison to other molecular ions the infrared transition probabilities are found to be rather small. For instance, the Einstein coefficient of spontaneous emission A¹₀ amounts to 1.63 s⁻¹ (CH⁺) and 0.19 s⁻¹ (CD⁺). Dipole moment functions of the neutral CH species in the X²Π and a⁴ Σ⁻ states have also been calculated and are compared with previous theoretical functions.     

High Compression-Induced Conductivity in a Layered Cu–Br Perovskite

We show that the onset pressure for appreciable conductivity in layered copper-halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10⁻⁴ S cm⁻¹, whereas here a Cu–Br congener, (EA)₂CuBr₄ (EA=ethylammonium), exhibits conductivity as high as 2×10⁻³ S cm⁻¹ at only 2.6 GPa, and 0.17 S cm⁻¹ at 59 GPa. Substitution of higher-energy Br 4p for Cl 3p orbitals lowers the charge-transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High-pressure X-ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression-induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression-induced conductivity of Cu-halide perovskites to more technologically accessible pressures.     

The energetics of ions,atoms, and salts: Sodium and its chloride

In this study we reconcile three seemingly contradictory assertions regarding sodium chloride. First, gaseous sodium chloride is Coulombically bound and highly ionic. Second, upon pulling the molecule apart atomic sodium and chlorine are produced. This is somewhat surprising; despite the high ionicity of NaCl, since IP(Na) > EA(Cl). Third, heterolytically dissociating NaCl(g) into Na⁺+Cl⁺ costs more energy than ionizing gaseous Na into Na⁺+e^?. Does this violate Coulomb's law since the Na-Cl bond distance in NaCl(g) is greater than the average Na nucleus-valance electron distance?     

Ionization energies of hypervalent Li2F,Li2Cl and Na2Cl molecules obtained by surface ionization electron impact neutralization mass spectrometry

Ionization energies of hypervalent Li(2)F, Li(2)Cl and Na(2)Cl molecules detected by surface ionization electron impact neutralization mass spectrometry are reported. The ionization energies were 3.78 +/- 0.2 eV for Li(2)F, 4.93 +/- 0.2 eV for Li(2)Cl, and 4.21 +/- 0.2 eV for Na(2)Cl. The ionization energies (IE) agree with theoretical ionization energies calculated by ab initio methods, supporting the theoretical prediction that Li(2)F has a hyperlithiated configuration in which the odd electron delocalizes over the two lithiums and with photoionization measurement. The first ionization energy of Na(2)Cl was experimentally confirmed earlier and for Li(2)Cl as well.8 We have developed and used this new approach for the problem--in the present work ions were first formed by surface ionization, followed by electron attachment (neutralization).     

The electronic structure of all-trans-polyenes C2nH2n+2, n = 3–7

The electronic structure of the C_2nH_2n+2 trans-polyenes, n = 3–7, is calculated by the Discrete Variational X_α method (DVM -X_α). The valence ionization potentials (IP ) calculated using the Clementi double zeta basis agree with the known experimental data within several tenths an electron volt. However, the DVM energies of the π → π* optical excitations are systematically underestimated by 0.8–1.0 eV. For polyenes with equal C—C bond lengths, the computed energies of the first optical transitions are smaller than those of polyenes with alternating C—C bond lengths. The charge distribution in polyenes is analyzed in the framework of a Mulliken scheme. The composition of the frontier molecular orbitals (MO ) is analyzed.     

A semi-empirical MO theory for ionization potentials and electron affinities. II. Vertical and adiabatic values,benzenoid and nonbenzenoid aromatic hydrocarbons,and conjugated molecules with heteroatoms

Further developments of a recent semiempirical, variable effective charge MO theory for calculation of ionization potentials (IP ) and electron affinities (EA ) as energy differences between separately minimized ground and ionized states are reported. The method is extended to adiabatic as well as vertical IPS and EAS by including core repulsion and σ bond compression energies in the total energy. The method is generalized to heteroatomic systems and is simplified by neglecting penetration integrals. As before, only two molecular parameters, the vertical IPS of benzene and naphthalene, are required to set the magnitude of the σ changes associated with the polarization of the core during loss or gain of a π charge. Twenty-seven aromatic molecules are studied, including polyacenes, condensed ring compounds, nonbenzenoids with five and seven member rings, nonplanar molecules, and heteroatomics with N⁺, as in pyridine, N⁺², as in pyrrole, and O⁺², as in furan. The results are within 0.2 eV of the photoelectron spectroscopic vertical IPS and the predicted vertical-adiabatic separation is consistent with the shape of the first band. The calculated EAS are within 0.2 eV of the observed values. The calculation is used to predict the IP and EA of the ionic photosensitizing cyanine dye, pinacyanol. The values obtained are consistent with the latest measured IP and EA of the adsorbed dye, corrected for surface and aggregation polarization effects.     

Theoretical study of spectroscopic parameters of alkali -Al and alkaline earth-Al dimers

The ground states of alkali-Al dimers (AlLi, AlNa, AlK, AlRb and AlCs) and alkaline earth-Al dimers (AlBe, AlMg, AlCa, AlSr and AlBa) along with their monovalent anions and cations were assigned based on the results of calculations. Bond lengths r _e , harmonic vibrational frequencies ω _e and dissociation energies D ₀ of these species were obtained. For neutral dimers, we also calculated adiabatic electron affinities (EA) and adiabatic ionization energies (IE). The present results are in agreement with the available experimental and other theoretical data. The ground state symmetry of AlLi, AlNa, AlK, AlRb and AlCs is ¹ Σ⁺. The ground state symmetry of AlBe⁺, AlMg⁺, AlCa⁺, AlSr⁺ and AlBa⁺ is also ¹Σ⁺. The ground state of AlLi^?, AlNa^?, AlK^?, AlRb^? and AlCs^? is ² Π, and is the same as in the isoelectronic neutral Al-alkaline-earth dimers. For both the alkali-Al and alkaline earth-Al neutral AlX species, the bond length increases monotonously with increasing atomic number of X. For the alkali-Al ions, energies of dissociation via the channels AlX^? → Al + X^? and AlX⁺ → Al + X⁺ are smaller than the energies of dissociation via the channel AlX^? → X + Al^? andAlX⁺ → X + Al⁺, respectively. While the opposite dissociation manner is found for alkaline earth-Al anions.     

Combining Zinc Phthalocyanines,Oligo(p-Phenylenevinylenes), and Fullerenes to Impact Reorganization Energies and Attenuation Factors

A study on electron transfer in three electron donor-acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as the excited-state electron donor and a fullerene (C₆₀) as the ground-state electron acceptor. These complexes are brought together by axial coordination at ZnPc. The key variable in our design is the length of the molecular spacer, namely, oligo-p-phenylenevinylenes. The lack of appreciable ground-state interactions is in accordance with strong excited-state interactions, as inferred from the quenching of ZnPc centered fluorescence and the presence of a short-lived fluorescence component. Full-fledged femtosecond and nanosecond transient absorption spectroscopy assays corroborated that the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state formation comes at the expense of excited-state interactions following ZnPc photoexcitation. At a first glance, the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state lifetime increased from 0.4 to 86.6 ns as the electron donor-acceptor separation increased from 8.8 to 29.1 Å. A closer look at the kinetics revealed that the changes in charge-separated state lifetime are tied to a decrease in the electronic coupling element from 132 to 1.2 cm⁻¹, an increase in the reorganization energy of charge transfer from 0.43 to 0.63 eV, and a large attenuation factor of 0.27 Å⁻¹.     

The electronic structure of weakly bound systems. II. NeX+ and ArX+(X = H2O,HCl, and HF) bimolecular cations

The theoretical framework developed and tested in our previous study of weakly bound systems is applied to a sequence of bimolecular cations: (NeX)⁺ and (ArX)⁺, where X = HF, H₂O, and HCl. The equilibrium structure, binding energies, and vibrational frequencies for this sequence of bimolecular cations are computed using several post-Hartree-Fock methods and triple zeta basis sets. In all cases, the absolute minima in the potential energy surface involves a hydrogen bond. The existence and stability of the aforementioned systems are established with binding energies ranging from 0.1 eV to 1.0 eV. The stability for the systems is explained in terms of the possible dissociative channels and changes in the electron density of the constituent monomers. © 1995 by John Wiley & Sons, Inc.     

Synergistic Engineering of Defects and Heterostructures Enhance Lithium/Sodium Storage Properties of F-SnO2-x-SnS2-x Nanocrystals Supported on N,S-Graphene

Phase engineering of the electrode materials in terms of designing heterostructures, introducing heteroatom and defects, improves great prospects in accelerating the charge storage kinetics during the repeated Li⁺/Na⁺ insertion/deintercalation. Herein, a new design of Li/Na-ion battery anodes through phase regulating is reported consisting of F-doped SnO₂-SnS₂ heterostructure nanocrystals with oxygen/sulfur vacancies (V_O/V_S) anchored on a 2D sulfur/nitrogen-doped reduced graphene oxide matrix (F-SnO_2-x-SnS_2-x@N/S-RGO). Consequently, the F-SnO_2-x-SnS_2-x@N/S-RGO anode demonstrates superb high reversible capacity and long-term cycling stability. Moreover, it exhibits excellent great rate capability with 589 mAh g⁻¹ for Li⁺ and 296 mAh g⁻¹ at 5 A g⁻¹ for Na⁺. The enhanced Li/Na storage properties of the nanocomposites are not only attributed to the increase in conductivity caused by V_O/V_S and F doping (confirmed by DFT calculations) to accelerate their charge-transfer kinetics but also the increased interaction between F-SnO_2-x-SnS_2-x and Li/Na through heterostructure. Meanwhile, the hierarchical F-SnO_2-x-SnS_2-x@N/S-RGO network structure enables fast infiltration of electrolyte and improves electron/ion transportation in the electrode, and the corrosion resistance of F doping contributes to prolonged cycle stability.     

Structure and bonding in simple thiazyl compounds

The molcules NSF, NSO⁻, NSCl, HNSF⁺, HNSO, CH₃NSF⁺, CH₃NSO are investigated at the SCF level and partly with inclusion of electron correlation effects. Equilibrium geometries and relative stabilities of isomers and conformers are reported. Structure constants and relative energies are discussed in connection with the molecular electronic structure as characterized by the results of population analyses.