Effect of aggregation on the excited-state electronic structure of perylene studied by transient absorption spectroscopy

The effect of aggregation on the excited-state electronic structure of perylene was studied through transient absorption measurements of isolated molecules, excimers, monomeric crystals (beta-perylene), and dimeric crystals (alpha-perylene). Changes of electronic state were clearly identified from the changes in transient absorption spectra. A detailed investigation was made by combining the obtained results with previous measurements of ground-state absorption and fluorescence spectra. The energy level of the ion-pair state in alpha-perylene crystals was estimated, and the results are compared with previous photoconductivity results. Moreover, the relaxation processes of excited states in alpha-perylene crystals were studied by femtosecond transient absorption measurements.     

Lithium intercalation of phenyl-capped aniline dimers: a study by photoelectron spectroscopy and quantum chemical calculations

Structural and electronic properties of pristine and lithium-intercalated, phenyl-capped aniline dimers as a model for the lithium-polyaniline system have been studied by photoelectron spectroscopy and quantum chemical calculations. It was found that the electronic structure of reduced and oxidized forms of oligoanilines is only weakly affected by isomerism. Upon intercalation, charge transfer from the Li-atoms is remarkable and highly localized at N-atomic sites, where configurations are energetically favored in which both N atoms of the dimers are bound to Li atoms. Conversion of nitrogen sites is different for the two forms of aniline dimers and incomplete up to high intercalation levels, indicating a pronounced role of solid-state effects in the formation of such compounds.     

Electronic structure of Li-intercalated oligopyridines: a comparative study by photoelectron spectroscopy

The role of nitrogen in the charge transfer and storage capacity of lithium-intercalated heterocyclic oligophenylenes was investigated using photoelectron spectroscopy. The development of new occupied states at low binding energies in the valence band region, as well as core level chemical shifts at both carbon and nitrogen sites, demonstrates partial charge transfer from lithium atoms to the organic component during formation of the intercalated compound. In small compounds, i.e., biphenyl and bipyridine derivatives, the position of the nitrogen heteroatom significantly affects the spacing between gap states in the Li-intercalated film; yet it has minimal effects on the charge storage capacity. In larger, branched systems, the presence of nitrogen in the aromatic system significantly enhances the charge storage capacity while the Li-N bond strength at high intercalation levels is significantly weakened relative to the nitrogen-free derivative. These observations have strong implications towards improved deintercalation processes in organic electrodes in lithium-ion batteries.     

双空位缺陷双层石墨烯储钠性能的第一性原理研究

采用基于密度泛函理论(DFT)的色散修正方法,研究了Na吸附和嵌入在双空位缺陷(DV)双层石墨烯(BLG)体系中的形成能、电荷转移、电极电势和扩散行为。形成能计算表明,无论单个Na原子在BLG表面吸附还是层间嵌入,均在DV空位中心处更稳定。电荷密度分布和Bader电荷计算表明Na与BLG的结合方式表现出离子性。Na嵌入DV缺陷BLG层间,缺陷浓度增加使BLG由AB堆垛向AA堆垛转变过程推迟;使Na在DV缺陷BLG的表面和层间能够稳定储钠的容量之和增至262.75 mAh?g~(-1),对应浓度Na与C摩尔比为2:17,储钠浓度继续增加,Na在BLG表面吸附容易产生枝晶或团簇。当层间嵌入Na原子时,表面Na原子向DV缺陷中心方向扩散能垒减小、表面Na原子沿相反方向的扩散能垒增加,DV缺陷的存在提高了BLG表面捕获Na的能力。     

有机化合物对电感耦合等离子体质谱(ICP-MS)法测定食品中总砷的影响

目的 研究有机化合物对电感耦合等离子体质谱法（ICP-MS）测定食品中总砷的影响,分析总结一般规律,为食品中总砷的准确测定提供理论依据。方法 研究了甲醇和乙醇等14种有机化合物对ICP-MS测定砷的动能歧视模式（KED）信号值和动态反应模式（DRC）信号值的影响,通过分析各有机化合物的电离能、极性和溶解度等性质,推测其在ICP-MS测定体系中对砷响应信号值增敏或者抑制的可能机理。结果 有机化合物对ICP-MS的KED模式测定砷离子As+的信号值有增敏效应,对DRC模式测定氧化砷离子AsO+信号值的影响小于KED模式测定As+的信号值,而且过程也更为复杂。相反,氮氧化物会减弱As+和AsO+的信号值。锗、铟等内标元素原子与砷原子在等离子体中电离行为和灵敏度的差异,使得内标元素校准砷测定信号的漂移受到干扰。结论 推测有机化合物影响ICP-MS测定砷响应信号值的可能机理是：有机化合物和氮氧化物经电离或裂解之后分别生成碳离子或多原子碳离子和氮氧离子或氮氧基团,碳离子或多原子碳离子会与砷原子发生电荷转移反应,增强As+或AsO+的信号值,同时有机化合物也可能会与As+竞争氧气而降低AsO+的信号值,而具有强电负性的氮氧基团可能会与As+和AsO+发生电荷转移反应而减弱其信号值。有机化合物对砷的ICP-MS响应信号值的影响可能是受到有机化合物电离能、溶解度、极性和分子结构等综合因素的结果。     

Photoionization dynamics of glycine adsorbed on a silicon cluster: "on-the-fly" simulations

Dynamics of glycine chemisorbed on the surface of a silicon cluster is studied for a process that involves single-photon ionization, followed by recombination with the electron after a selected time delay. The process is studied by "on-the-fly" molecular dynamics simulations, using the semiempirical parametric method number 3 (PM3) potential energy surface. The system is taken to be in the ground state prior to photoionization, and time delays from 5 to 50 fs before the recombination are considered. The time evolution is computed over 10 ps. The main findings are (1) the positive charge after ionization is initially mostly distributed on the silicon cluster. (2) After ionization the major structural changes are on the silicon cluster. These include Si-Si bond breaking and formation and hydrogen transfer between different silicon atoms. (3) The transient ionization event gives rise to dynamical behavior that depends sensitively on the ion state lifetime. Subsequent to 45 fs evolution in the charged state, the glycine molecule starts to rotate on the silicon cluster. Implications of the results to various processes that are induced by transient transition to a charged state are discussed. These include inelastic tunneling in molecular devices, photochemistry on conducting surfaces, and electron-molecule scattering.     

Core ionization energies and multi-peak structure of esca bands in some pentatomic heterocyclic compounds

The core ionization energy and the multi-peak structures of ESCA bands in furan, pyrrole, thiophen and their saturated homologues were obtained. Significant change of ESCA data is observed on going from the saturated to the aromatic compounds. The variations in the core ionization energies seem connected to the mesomeric drift of charge from the heteroatom to the carbon atoms in the aromatic derivatives. Shake-up processes involving charge-transfer transitions are considered to be the major responsible of the observed multi-peak structure in the aromatic compounds.     

Sodium adduct formation efficiency in ESI source

Formation of sodium adducts in electrospray (ESI) has been known for long time, but has not been used extensively in practice, and several important aspects of Na⁺ adduct formation in ESI source have been almost unexplored: the ionization efficiency of different molecules via Na⁺ adduct formation, its dependence on molecular structure and Na⁺ ion concentration in solution, fragmentation behaviour of the adducts as well as the ruggedness (a prerequisite for wider practical use) of ionization via Na⁺ adduct formation. In this work, we have developed a parameter describing sodium adducts formation efficiency (SAFE) of neutral molecules and have built a SAFE scale that ranges for over four orders of magnitude and contains 19 compounds. In general, oxygen bases have higher efficiency of Na⁺ adducts formation than nitrogen bases because of the higher partial negative charge on oxygen atoms and competition from protonation in the case of nitrogen bases. Chelating ability strongly increases the Na⁺ adduct formation efficiency. We show that not only protonation but also Na⁺ adduct formation is a quantitative and reproducible process if relative measurements are performed. Copyright © 2013 John Wiley & Sons, Ltd.     

Density functional study of structural and electronic properties of small bimetallic silver-nickel clusters

Theoretical study on the structure and electronic properties of small AgmNip (m + p < or = 6) clusters has been carried out in the framework of density functional theory. Structural features, cohesive energies, vertical ionization potentials, and charge transfers are evaluated for each Ag/Ni ratio. In all the AgmNip clusters, the nickel atoms are brought together, yielding a maximum of Ni-Ni bonds, and the silver atoms are located around a Ni core with a maximum of Ag-Ni bonds. The ionization potential and the highest occupied molecular orbital shape are directly related to the two- or three-dimensional character of the cluster's geometry. A very low electronic charge transfer from Ni to Ag is found, and the magnetic moment is located on Ni atoms but with a low spin polarization on silver in the Ni-rich clusters.     

Trapping molecular ions formed via photo-associative ionization of ultracold atoms

The formation of (40)Ca(2)(+) molecular ions is observed in a hybrid (40)Ca magneto-optical and ion trap system. The molecular ion formation process is determined to be photo-associative ionization of ultracold (40)Ca atoms. A lower bound for the two-body rate constant is found to be beta ≥ 2 ± 1 × 10(-15) cm(3) Hz. Ab initio molecular potential curves are calculated for the neutral Ca(2) and ionic Ca(2)(+) molecules and used in a model that identifies the photo-associative ionization pathway. As this technique does not require a separate photo-association laser, it could find use as a simple, robust method for producing ultracold molecular ions.     

Intercalation of trioxatriangulenium ion in DNA: binding,electron transfer,x-ray crystallography,and electronic structure

Trioxatriangulenium ion (TOTA(+)) is a flat, somewhat hydrophobic compound that has a low-energy unoccupied molecular orbital. It binds to duplex DNA by intercalation with a preference for G-C base pairs. Irradiation of intercalated TOTA(+) causes charge (radical cation) injection that results in strand cleavage (after piperidine treatment) primarily at GG steps. The X-ray crystal structure of TOTA(+) intercalated in the hexameric duplex d[CGATCG](2) described here reveals that intercalation of TOTA(+) results in an unusually large extension of the helical rise of the DNA and that the orientation of TOTA(+) is sensitive to hydrogen-bonding interactions with backbone atoms of the DNA. Electronic structure calculations reveal no meaningful charge transfer from DNA to TOTA(+) because the lowest unoccupied molecular orbital of TOTA(+), (LUMO)(T), falls in the gap between the highest occupied molecular orbital, (HOMO)(D), and the (LUMO)(D) of the DNA bases. These calculations reveal the importance of backbone, water, and counterion interactions, which shift the energy levels of the bases and the intercalated TOTA(+) orbitals significantly. The calculations also show that the inserted TOTA(+) strongly polarizes the intercalation cavity where a sheet of excess electron density surrounds the TOTA(+).     

Positron annihilation studies of some charge transfer molecular complexes

Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes.

The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred from the IR-spectral data.     

Strong-field ionization and dissociation studies on small early transition metal carbide clusters via time-of-flight mass spectrometry

In this work, we report experimental results from the strong-field ionization and subsequent Coulomb explosion of narrow distributions of small (<40 atoms) heteronuclear clusters composed of transition metal (Ti, V, Cr, Nb, or Ta) and carbon atoms. Analysis of the resulting multiply charged ions was performed through time-of-flight mass spectrometry, and evidence regarding ionization dynamics was obtained. The data reveal the presence of enhanced ionization during exposure to the ultrashort (～100 fs) pulse resulting in the formation of ions possessing significantly higher charge states than those predicted from atomic species. Regardless of the transition metal species, we observe the absorption of similar amounts of energy from the external field, as indicated by the maximum observed charge states in each experiment. These results are compared to our previously reported study on the strong-field ionization of transition metal oxide clusters. We observe identical maximum observable charge states for each of the transition metal species resulting from both metal oxide and metal carbide clusters.     

有机紫外吸收剂插层锌铝水滑石的制备及表征

采用离子交换法，以去离子水或乙二醇为分散介质，制备了层间为磺基水杨酸、4-羟基-3-甲氧基肉桂酸和2-羟基-4-甲氧基二苯甲酮-5-磺酸等紫外吸收剂阴离子插层的锌铝水滑石。利用XRD、IR、TG-DTA等技术对样品结构进行表征，采用UV-Vis吸收光谱研究产物的光化学特性，并用Gaussian-98软件包中ab initio分子轨道法(HF/6-31G)计算了3种有机紫外吸收剂的分子结构和电荷分布，提出了合理的客体分子在主体层间的排列方式，分析了其结构与光化学行为的关系。研究表明，由于有机紫外吸收剂进入层间，不仅客体与主体层板存在静电力和氢键相互作用，而且在限域空间中有利于客体之间的相互作用，从而使插层产物的紫外吸收范围和能力显著增强，是一类具有潜在应用价值的无机-有机超分子复合结构的紫外吸收材料。     

Nitrogen-rich oligoacenes: candidates for n-channel organic semiconductors

The successive replacement of CH moieties by nitrogen atoms in oligoacenes (benzene to hexacene) has been studied computationally at the B3LYP/6-311+G(d,p)//6-31G(d) level of theory, and the effects of different heteroatomic substitution patterns on structures, electron affinities, excitation, ionization, and reorganization energies are discussed. The calculated tendencies are rationalized on the basis of molecular orbital arguments. To achieve electron affinities of 3 eV, a value required to allow for efficient electron injection from common metal electrodes, at least seven nitrogen atoms have to be incorporated into tetracenes or pentacenes. The latter require rather small reorganization energies for electron transfer (<0.20 eV) making these compounds promising candidates for n-channel semiconducting materials. Particularly interesting are heptaazapentacenes 5 and 6 in which the nitrogen atoms are arranged to form self-complementary systems with a maximum number of intermolecular CH-N contacts in planar oligomers. These interactions are expected to facilitate the formation of graphite-like sheet structures with cofacial arrangements of the pi systems and short interlayer distances due to attractive N-C(H) interlayer interactions. This should not only be ideal for charge transfer but also might contribute to improved air stability of these semiconductors. Self-complementarity is maintained in azaacenes containing two cyano groups in the terminal rings. These compounds require lower reorganization energies than the unsubstituted heterocycles (0.13-0.14 eV), show high electron affinities (3.3 eV), and are thus promising candidates for materials applications.     

Mass spectrometric study of 9-substituted 10-sila-2-azaanthracenes

The dissociative ionization of 10 derivatives of 10-sila-2-azaanthracene, containing cyanoethyl (I–III), aminopropyl (IV), amino (V, VI), and amide (VII–X) groups at the C₍₉₎ atom, was investigated. It was shown that for all the compounds the general direction of decomposition is elimination of substituents from the silicon and carbon C₍₉₎ atoms. The stability of the compounds to electron impact is determined chiefly by the nature of the substituent at the C₍₉₎ atoms and depends weakly on the type of substituent at the silicon atom. In the case of amino-derivatives V–X, fragmentation of the molecular ions is determined by the method of localization of the positive charge in the molecular ion. This determines the occurrence of specific decompositions, which permits reliable identification of the compounds studied according to their mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1071–1076, August, 1984.     

Electrospray ionization-multistage tandem mass spectrometry of complex multitin organometallic compounds

The series of 14 complex organotin(IV) compounds containing many tin atoms and noncovalent bonds in the structure was characterized by electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). The mass spectra were measured in both polarity modes to obtain complementary structural information. The characteristic pattern of ten natural tin isotopes allowed the determination of the number of tin atoms in the molecular adducts and fragment ions by comparing theoretical and experimental isotopic distributions. Positive ion ESI spectra show unusual adduct formation depending on the type of organic solvent used for the direct infusion analysis owing to the ion-molecule reactions in the ion source. On the basis of the detailed spectral interpretation of organotin(IV) compounds, the fragmentation patterns of multitin organometallic compounds have been proposed. Noncovalent bonds in polymeric complexes are fragmented first, which is then followed by characteristic neutral losses in monomeric units.     

The kinetic energy of molecular charge distributions and molecular stability

This paper examines the relationship between the topographical features of a molecular charge distribution and the kinetic energy of the system. Specifically, the spatial contributions to the kinetic energy are related to the Laplacian of the total charge density and to the gradients of the natural-orbital densities. It is concluded that a necessary requirement for molecular stability is the existence of a net negative curvature for the molecular charge distribution in the internuclear region. It is shown that the charge density accumulated in the internuclear region of a stable molecule is distributed in such a way as to keep the accompanying increase in the kinetic energy to a minimum. A comparison of the contributions to the kinetic energy from the atomic and molecular charge distributions indicates that in the formation of a stable molecule the contribution from the molecular charge density in the binding region is decreased relative to that of the atoms.     

烷烃电离能和生成焓的相关性

根据化合物形成过程中价电子能量变化与生成焓之间的关系, 推导出烷烃的生成焓和电离能之间的关系. 以21个烷烃化合物为模型将实验测定的电离能与标准生成焓进行直接关联, 证实了模型方程的适用性, 所得回归方程的相关系数达到0.9999, 估算值与实验值之间的标准偏差仅为0.03 eV. 同时还利用实验测定的标准生成焓对一系列烷烃的电离能作了预测.