第二过渡周期金属单氧化物电子结构的DFT表征

文章采用九种密度泛函方法系统地研究了第二过渡周期金属单氧化物及其正负离子的键长,频率,电离能,电子亲和势及解离能。     

Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W,Mo, Ru,Co)

The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au₁₀ (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au₁₀ (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au₁₀ cluster. In addition, the large HOMO–LUMO gaps suggest that the M@Au₁₀ (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au₁₀ and Mo@Au₁₀ clusters have electron affinities similar to the super-halogen Al₁₃.     

Shell Effects in the Relaxation Energy of 2s-Core Ionization of Atoms from B through Xe

In this paper we investigate the variation, along the periodic table, of 2s-core ionization energies, using both relativistic and non-relativistic calculations. We show that electron relaxation energies display variations typical of the shell-filling process, while their relativistic contributions show specifically distorted shell features. Just as for the 1s-core ionization energies, investigated earlier, the sensitivity of these differential properties to the shell-filling process may be used as a probe of the accuracy of calculations of core ionization energies. Discrepancies with experimental results are critically analyzed.     

Negative ion processes for the unambiguous identification of polycyclic aromatic compounds

Electron capture negative ion processes have been applied to the determination of polycyclic aromatic hydrocarbons in complex mixtures using both chemical ionization mass spectrometry and a newly developed gas chromatographic detector. The negative ion chemical ionization mass spectrometric technique allows isomeric PAH compounds to be differentiated on the basis of relative electron affinities. Compounds which have electron affinities > 0.5 eV form molecular anions while compounds with lower electron affinities are not ionized. The new gas Chromatographic detector also enables isomeric PAH to be differentiated as a function of relative electron affinities. This detector exhibits continuous tunability, allowing the gas phase reactions to be controlled to a greater degree than in the NICI experiment. This flexibility allows a wider variety of compounds to be differentiated using the g.c. detector. Additionally, the g.c. detector may be operated either as a conventional electron capture detector or as an argon ionization detector, which has virtually universal response to organics.     

Double and Triple Differential Cross Sections for Single Ionization of Benzene by Electron Impact

Experimental results for the electron impact ionization of benzene, providing double (DDCS) and triple differential cross sections (TDCS) at the incident energy of 90 eV, measured with a multi-particle momentum spectrometer, are reported in this paper. The most intense ionization channel is assigned to the parent ion (C₆H₆⁺) formation. The DDCS values are presented for three different transferred energies, namely 30, 40 and 50 eV. The present TDCS are given for two fixed values of the ejected electron energy (E₂), at 5 and 10 eV, and an electron scattering angle (θ₁) of 10°. Different features related to the molecular orbitals of benzene from where the electron is extracted are observed. In addition, a semi-empirical formula to be used as the inelastic angular distribution function in electron transport simulations has been derived from the present DDCS result and compared with other expressions available in the literature.     

卤代甲醛的电离势和电子亲和势的理论研究

利用B3LYP,HF,MP2,MP3和CCSD(T)方法在6-311++G**基组上研究了卤代甲醛在气相中的绝热电离势和绝热电子亲和势。为了描述环境介质的影响,利用MP2/6-311++G**理论研究了卤代甲醛在氯仿、丙酮、硝基甲烷和水中的绝热、垂直电离势和绝热、垂直电子亲和势以及重组能。所有的电离势无论是在气相还是在液相中都是正值,并且液相中的电离势值比气相中的小且随着溶剂介电常数的增大而减小。在MP2/6-311++G**理论上算出的所有的卤代甲醛在气相中的绝热和垂直电子亲和势都是负值,而在液相中却全都变成了正值且随着溶剂介电常数的增大而增大。     

Electrochemical and DFT-studies of substituted thiophenes

UV-vis absorption spectra and cyclic voltammograms of a selection of substituted thiophenes and their oligomers carrying trifluoracetyl acetone functional groups have been obtained. A comparison with calculated values of HOMO-LUMO energies (the former corresponding to the ionization potentials E_i) shows strong correlations between calculated and experimentally obtained data; they are in close agreement with estimates in terms of electron-donating and -withdrawing effects from an empirical point of view.     

Determination of the Boron and Phosphorus Ionization Energies in Compensated Silicon by Temperature-Dependent Luminescence

The determination of boron and phosphorus ionization energies in compensated silicon is very important for assessing the ionization level of dopants and their interaction with each other. In this paper, we achieved the boron and phosphorus ionization energies in compensated silicon by temperature-dependent luminescence for the first time. The results show that the boron and phosphorus ionization energies in heavily-compensated silicon have the same values as those in non-compensated silicon. This strongly suggests that both boron and phosphorus impurities with a concentration of ≤ 10 ¹⁷ cm ^?3 should act as isolated acceptors and donors, but do not form complexes in silicon.     

Binding Energies of Aromatic 1:1 Hetero-Clusters in a Supersonic Jet

Methods used to experimentally estimate the binding energies of van der Waals clusters containing an aromatic molecule are surveyed. These include microwave and infrared absorption spectroscopies, single and two photon ionization, dispersed fluorescence, and stimulated emission pumping. The problems encountered in the application of these methods are briefly discussed, and prospects for the firm establishment of the binding energies are assessed. Although the present database is too small for firm conclusions, methods based on dispersed fluorescence (i.e., probing the excited state surface) tend to yield lower values for argon adducts than those based on ionization, probing the ground state, or ionic surfaces. A mechanism that may account for this tendency is proposed, and further experiments are proposed to test it.     

Hyperthermal Surface Ionization

Surface ionization of molecules with hyperthermal kinetic energy (1–20 eV) was found to be very efficient, demonstrating several unique features. We have used the technique of aerodynamic acceleration in supersonic seeded beams in order to obtain molecular kinetic energies in the range 1–20 eV. Three types of hyperthermal surface ionization (HSI) processes were observed: (a) surface-molecule electron transfer was demonstrated in the I₂/diamond system where negative molecular iodine (I⁻₂) ions were produced; (b) molecule-surface electron transfer was found for the anthracene molecule where positive molecular anthracene ions were generated; (c) hyperthermal surface-induced dissociative ionization (HSIDI) was observed in 1-iodopropane, 1-chloro-3-iodopropane, benzyl bromide, and many other molecules. In these processes, we have observed a large current of negative halogen ions and positive molecular residue ions (ion-pair formation). The mechanism of HSI is described in terms of electron transfer processes. It occurs due to a curve crossing between the neutral scattering interaction potential surface and the ionic interaction potential surface and nonunity reneutralization second curve crossing of the scattered molecules or fragment ions.     

Theoretical investigation on the ground- and excited-state properties of novel octupolar oligothiophene-functionalized truxenes and dipolar analogs

The density functional theory (DFT) is used to compute the ground-state geometries, ionization potentials (IPs), electron affinities (EAs) and HOMO-LUMO gaps (ΔE_H-L) of novel octupolar oligothiophene-functionalized truxenes and the corresponding dipolar analogs. The lowest singlet excited-state geometries of some oligomers have been investigated by the singles configuration interaction (CIS) method. The absorption and emission spectra are calculated by time-dependent DFT (TDDFT) on the basis of the ground- and excited-state geometries, respectively. Our calculations are in good agreement with the available experimental results. The calculated results show that all oligomers are nonplanar in their ground electronic states. The structural relaxation upon excitation results in the planarity of dipolar oligomers and one branch of octupolar oligomers. Because fluorene and truxene segments in two series are not the repeated units of oligomers, the chain dependence of IPs, EAs, ΔE_H-L and excitation energies do not follow the usual linear 1/n rule. We have used three plotted points closest to polymer to plot lines; and extrapolated the resultant linear relationship to infinite chain length; and finally obtained the relative properties of polymers.     

Measured activation energies of ignition of solid materials

Measured activation energies of ignition of a wide variety of solid materials of practical importance are tabulated. The Frank-Kamenetskii model of thermal ignition was used in their determination. Comments are made on the values in terms of the nature of the respective materials and in terms of the value of the measured quantities as input to mathematical simulation of ignition.     

Investigation of the Effect of Functional Group Substitutions on the Gas-Phase Electron Affinities and Ionization Energies of Room-Temperature Ionic Liquids Ions using Density Functional Theory

The cathodic and anodic stabilities of room-temperature ionic liquids (ILs) are important factors in their applications in electrochemical devices. In this work, we investigated the electron affinities of cations and ionization energies of anions for ionic liquids by density functional theory (DFT) calculations at the B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) level. Over 200 unique cations and anions, formed from a set of six base cation structures, three base anion structures, and seven functional groups, were investigated. We find the trends in calculated EAs of alkylated cations and IEs of alkylated anions to be in good agreement with observed experimental trends in relative cathodic and anodic stabilities of various ILs. In addition, we also investigated the effect that functional group substitution at distinct positions in the ions have on the EA of the 1,2,3-trimethylimidazolium cation and the IE of the PF₅CF₃ anion. The overall impact on the EA or IE can be explained by the known electron-donating and electron-withdrawing inductive and resonance effects of the attached functional group, and the relative strength of the effect depends on the substitution position.     

Three-Body Excitations in Fock-Space Coupled-Cluster: Fourth Order Perturbation Correction to Electron Affinity and Its Relation to Bondonic Formalism

In this paper, we present a formulation of highly correlated Fock-space multi-reference coupled-cluster (FSMRCC) methods, including approximate triples on top of the FSMRCC with singles and doubles, which correct the electron affinities by at least at third and up to the fourth order in perturbation. We discuss various partial fourth-order schemes, which are reliable and yet computationally more efficient than the full fourth-order triples scheme. The third-order scheme is called MRCCSD+T^*(3). We present two approximate fourth-order schemes, MRCCSD+T^*−a(4) and MRCCSD+T^*(4). The results that are presented allow one to choose an appropriate fourth-order scheme, which is less expensive and right for the problem. All these schemes are based on the effective Hamiltonian scheme, and provide a direct calculation of the vertical electron affinities. We apply these schemes to a prototype Li₂ molecule, using four different basis sets, as well as BeO and CH⁺. We have calculated the vertical electron affinities of Li₂ at the geometry of the neutral Li₂ molecule. We also present the vertical ionization potentials of the Li₂ anion at the geometry of the anion ground state. We have also shown how to calculate adiabatic electron affinity, though in that case we lose the advantages of direct calculation. BeO has been examined in two basis sets. For CH⁺, four different basis sets have been used. We have presented the partial fourth-order schemes to the EA in all the basis sets. The results are analyzed to illustrate the importance of triples, as well as highlight computationally efficient partial fourth-order schemes. The choice of the basis set on the electron affinity calculation is also emphasized. Comparisons with available experimental and theoretical results are presented. The general fourth-order schemes, which are conceptually equivalent with the Fock-space multi-reference coupled-cluster singles, doubles, and triplets (MRCCSD+T) methods, based on bondonic formalism, are also presented here in a composed way, for quantum electronic affinity.     

Correlation of physical and polymer chain properties

An idealized polymer model is used to examine the magnitude of the catastrophic tensile breaking energy and stress in terms of primary and secondary bonding forces. Computed strengths for primary and secondary bonding are respectively 8000 and 500 times larger than observed values of a common thermoplastic. From other considerations, the glass transition temperature for both elastomeric and thermoplastic polymers is found to show a linear dependence on the cohesive energy per unit length of polymer chain. In special polymer model, the influence of polymer chains on unidirectional elongation is shown to be a function of chain size. Elongation data reported on a series of modified polycarbonates exhibit a correlation with chain size as described by the model. Published data on the polycarbonate series are used to evaluate the correlation between observed deformation breaking energies and cohesive energies calculated from glass transition temperatures.     

The solvation of monatomic ions

The significance of plots of hydration enthalpies vs ionization potentials is questioned. Aqueous ionization enthalpies for transition-metal ions (crystal-field-corrected), and ionization potentials, are linearly related, but a hook sequence in similar plots for closed-shell species is remarked. Several other solution properties are shown to follow such a sequence, and the basis for this is discussed. The persistence of the hook relationship through many apparently dissimilar solvents is explained by the comparability of the solvent moieties. The solvation free energies of the alkali ions relative to the H⁺ values are shown to be largely determined by the H⁺-moiety interaction involving the protonic charge and average moiety polarizability.     

Characterization of stoichiometric adsorption complexes in H-ZSM-5 using microcalorimetry

We have used microcalorimetry to examine the stoichiometric adsorption complexes formed by ammonia, pyridine, and isopropylamine at the A1 sites in H-ZSM-5. The results show that the heats of adsorption for each adsorbate are constant up to a coverage of one molecule /Al, implying that all of the acid sites in H-ZSM-5 are equivalent in strength. The adsorption energies of the complexes formed by ammonia, pyridine, and isopropylamine were found to be 150, 200, and 240 kJ/mol, respectively. Comparison of these values with a simple potential-energy model which assumes that the heat of adsorption scales linearly with gas phase proton affinities suggests that proton transfer dominates the interaction between the adsorbate and the acid site, but that other factors must also be included.     

Determination of the ionization constant of water between 100 to 200°C by emf measurements,with some derived thermodynamic quantities

The first experimentally derived values of the ionization constant of water and associated thermodynamic quantities, by emf measurements, are reported, within the range 100–200°C. The derived values of the ionization constant of pure water from these measurements support the findings obtained by purely thermochemical observations. The effects of a recalculation of the observed discrepancies, both in the heats of ionization and molal heat capacity, between emf measurements and thermochemical values at 25°C are also discussed, by an appraisal of the empirical methods that are available and that have been used for the treatment of experimental data. A method, producing a new family of equations based on theoretical-structural considerations, is also suggested for the behaviour of the ionization constant of water as a function of temperature. Values for the heats of ionization of water between 100 and 200°C are also proposed.     

Analysis of Electrolyte Polarization in Polycrystalline Sodium β-Alumina by a Complex Admittance Method

The polarization behavior of lithia-stabilized sodium β-alumina in the form of polycrystalline pressed and sintered specimens was studied at 100° to 400°C by observing the isothermal values of the complex admittance from ≊5 Hz to 500 kHz. Analyzing these data in the complex admittance plane in terms of an equivalent circuit for the system made it possible, when ion-blocking electrodes were used, to distinguish the separate contributions of the grain boundaries and the bulk crystals to the total electrolyte resistance. These results gave activation energies of 0.32 to 0.41 eV for the grain-boundary resistance and 0.11 to 0.14 eV for the bulk resistance. The prefactors in the Arrhenius expressions for these resistances appeared to be more sensitive to factors such as specimen composition, microstructure, and specimen preparation conditions than are the activation energies.     

Effective Doping in Cubic Si3N4 and Ge3N4: A First-Principles Study

First-principles calculations have been conducted to investigate impurities in cubic Si₃N₄ and Ge₃N₄. Impurity species suitable for n - and p -type doping are suggested, in terms of the formation and ionization energies. The suggested species are P and O as n -type dopants and Al as a p -type dopant for c -Si₃N₄, and Sb and O as n -type dopants and Al as a p -type dopant for c -Ge₃N₄. The dependence of the formation energies on the chemical potentials indicates that a proper choice of growth conditions is mandatory for suppressing the incorporation of these impurities into anti and interstitial sites, where the impurities can be charged to compensate carriers.