Dissociation of alkane ionized molecules

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H⁺, He²⁺, and Ar⁶⁺ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1–25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.     

酸根离子及其水溶液对镎酰离子结构性质的影响

利用B3LYP杂化密度泛函方法,在相对论有效芯势模型下,优化得到了NpO_2~(2+)离子及其配合物在气相和水溶液中的几何结构和电子结构,研究了NO-3、SO2-4和CO2-3离子及其水溶液对NpO_2~(2+)离子的结构和性质的影响.结果表明,NpO_2~(2+)离子结合各种酸根离子后其Np=O键的键长都有明显增长、Np和O原子的价电子轨道能均有升高,而考虑溶剂化效应后酸根离子的影响将减小.电荷分析发现,结合酸根离子后,NpO_2~(2+)中Np和O原子间形成的共价键的强度减弱、键长增长.对NpO_2~(2+)离子与三种酸根离子的理论结合能的比较显示,Np O2CO3分子最为稳定.     

酸根离子及其水溶液对镎酰离子结构性质的影响

利用B3LYP杂化密度泛函方法,在相对论有效芯势模型下,优化得到了NpO22+离子及其配合物在气相和水溶液中的几何结构和电子结构, 研究了NO3-、SO42-和CO32-离子及其水溶液对NpO22+离子的结构和性质的影响.结果表明,NpO22+离子结合各种酸根离子后其Np=O键的键长都有明显增长、Np和O原子的价电子轨道能均有升高,而考虑溶剂化效应后酸根离子的影响将减小.电荷分析发现,结合酸根离子后,NpO22+中Np和O原子间形成的共价键的强度减弱、键长增长.对NpO22+离子与三种酸根离子的理论结合能的比较显示,NpO2CO3分子最为稳定.     

Solvent effects on chemical processes: new solvents designed on the basis of the molecular–microscopic properties of (molecular solvent + 1,3‐dialkylimidazolium) binary mixtures

The purpose of this work was to analyze the microscopic feature of binary solvent systems formed by a molecular solvent (acetonitrile or dimethylformamide or methanol) and an ionic liquid (IL) cosolvent [1‐(1‐butyl)‐3‐methylimidazolium tetrafluoroborate or 1‐(1‐butyl)‐3‐methylimidazolium hexafluorophosphate]. The empirical solvatochromic solvent parameters E_T(30), π*, α, and β were determined from the solvatochromic shifts of adequate indicators. The behavior of the solvent systems was analyzed according to their deviation from ideality. The study focused on the identification of solvent mixtures with relevant solvating properties in order to select mixed solvents with particular characteristics. The comparison of the molecular–microscopic solvent parameters corresponding to the selected binary mixtures with both ILs considered at similar mixed‐solvent composition revealed that the difference is centered on the basic character of them. A kinetic study of a nucleophilic aromatic substitution reaction between 1‐fluoro‐2,4‐dinitrobenzene (FDNB) and 1‐butylamine (BU) developed in (acetonitrile or dimethylformamide + IL) solvent mixtures is presented in order to investigate and compare the solvent effects on a chemical process. For the explored reactive systems the solvation behavior is dominated by both the dipolarity/polarizability and the basicity of the media, contributing these solvent properties to accelerating the chemical process. Copyright © 2007 John Wiley & Sons, Ltd.     

ScH~+和ScH_2~+分子离子的结构与势能函数(英文)

本文利用相对论有效原子实势(RECP)和密度泛函(B3PW91)的方法对ScH 和ScH2 分子离子的结构进行了优化,得到了它们的平衡几何构型和谐振频率.采用最小二乘法拟合出ScH 分子离子的Murrell-Sorbie势能函数,在此基础上,推导出光谱数据和力常数,并通过多体展式理论导出ScH2 分子离子的势能函数,其等值势能面图准确地再现了ScH<,2< 分子离子的结构特征和离解能,由此讨论了反映势能面的静态特征,并利用杂化轨道理论解释了ScH2 分子离子的结构.     

Theoretical study on the molecular tautomerism of the 3-hydroxy-pyridin-4-one system

3-hydroxy-pyridin-4-one is a parent molecule for the family of hydroxypyridinones that are known in coordination chemistry as efficient metal ions chelators. In this work, relative stabilities of some possible tautomers were investigated using several quantum chemical methods: CBS (complete basis set methods), Gn, DFT (density functional theory), Hartree–Fock and MP2. Performed calculations show that the system under consideration exists as a mixture of two tautomers with comparable energies. Among them, the hydroxypyridinone structure of the studied molecular system seems to be a bit more stable than the o-dihydroxypyridine one, by a few kJ/mol only. Aromaticity and intra-molecular hydrogen bonding are the main effects influencing the stability of the studied tautomeric structures. Consequently, aromatic effects were calculated using several indices of aromaticity: HOMA (harmonic oscillator model of aromaticity), NICS (nucleus independent chemical shift), H, PDI (para delocalisation index), MCI (multi-centre index) and ASE (aromatic stabilisation energy). The strength of possible intra-molecular hydrogen bonds (H-bonds) was determined by means of the AIM (atoms-in-molecules) method and by calculating enthalpies for theoretical reactions that do or do not involve H-bonds. The AIM method was employed to understand how variations in atomic energies influence the stability of different tautomeric structures.     

Survival of He+ ions during grazing scattering from a Ag(111) surface

He+ ions as well as neutral He atoms with keV energies are scattered under a grazing angle of incidence from a clean and atomically flat Ag(111) surface. From a comparison of ion fractions observed after scattering of He+ ions and He atoms we find for energies below some keV small but defined fractions of ions that have survived the complete scattering event with the surface. This feature allows us to clear up the microscopic interaction scenario for Auger neutralization of He+ ions at a Ag(111) surface. The Auger neutralization rates are 2 to 3 orders of magnitude smaller than conventional rates derived from experiments for He+-metal systems and agree with recent calculations.     

Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches

The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.     

Charge driven fragmentation of nucleobases

We studied multiple ionization of single nucleobases by means of slow highly charged ions (Xe(q+), q=5-25). The products of the subsequent fragmentation were studied using high resolution coincidence time-of-flight spectrometry. We observed a strong dependence of the fragment kinetic energies on the initial charge state of the intermediate parent ions as well as on the initial chemical environment of the respective fragment ions within the parent molecule. The data allow us to shed light on the charge distribution within the molecule as well as on the fragmentation dynamics of these intermediate size systems.     

Electron-impact ionization and dissociative ionization of sulfur in the gas phase

We describe the methods and the results of investigation of the yield of positive ions formed as a result of electron-impact ionization of sulfur. The ionization energy for the basic molecule and the energies corresponding to the emergence of fragment ions are obtained from the ionization efficiency curves. The dynamics of formation of molecular sulfur ions in the temperature range 320–700 K is investigated. The energy dependences of efficiency S _n of the ion formation for n = 1–6 are analyzed, and their appearance energies are determined. The total cross section of sulfur ionization by a monochromatic electron beam is also investigated. Using the linear approximation method, we marked out features on the ionization function curve, which correspond to the ionization and excitation energies for multiply charged ions. The total cross section of the formation of negative sulfur ions is measured in the energy range 0–9 eV.     

Discrete Velocity Models for Polyatomic Molecules Without Nonphysical Collision Invariants

An important aspect of constructing discrete velocity models (DVMs) for the Boltzmann equation is to obtain the right number of collision invariants. Unlike for the Boltzmann equation, for DVMs there can appear extra collision invariants, so called spurious collision invariants, in plus to the physical ones. A DVM with only physical collision invariants, and hence, without spurious ones, is called normal. The construction of such normal DVMs has been studied a lot in the literature for single species, but also for binary mixtures and recently extensively for multicomponent mixtures. In this paper, we address ways of constructing normal DVMs for polyatomic molecules (here represented by that each molecule has an internal energy, to account for non-translational energies, which can change during collisions), under the assumption that the set of allowed internal energies are finite. We present general algorithms for constructing such models, but we also give concrete examples of such constructions. This approach can also be combined with similar constructions of multicomponent mixtures to obtain multicomponent mixtures with polyatomic molecules, which is also briefly outlined. Then also, chemical reactions can be added.     

用宏观-微观模型系统计算偶-偶超重核基态性质

用宏观--微观模型系统计算了Z=94—112偶偶超重核的基态性质. 其中宏观部分基于液滴模型, 微观部分采用改进的谐振子势. 理论计算的结合能、α衰变能 与已知的实验数据符合, 理论计算结果也与Moller的计算结果符合很好.这肯定了宏观--微观模型对超重核性质研究的可靠性和稳定性. 对一些未知核素基态性 质的预言可为将来的实验研究提供理论参考.     

The interaction energy of three molecules united in a nanocluster by long-range attraction forces with account for Coulomb repulsion

The interaction energy of three neutral molecules that form a nanocluster is studied. It is assumed that one molecule (M₀) has a dipole moment, while the other two (M₁ and M₂) are nonpolar. The molecule interaction energy in such a nanocluster is determined by the sum of dispersion interaction energies of each pair of molecules and the sum of inductive energies of the molecules. Analytical expressions for these energies as functions of the distance between the centers of mass of the molecules have been obtained. A method for the determination of damping functions which takes the contribution of repulsive forces into account has been developed. Analytical expressions for the molecule interaction energies for a two-molecule cluster in an external field of the third molecule have been obtained. A nanocluster consisting of a molecule of polar isomer pentene C₅H₁₀ and a nonpolar molecule of polycyclic aromatic hydrocarbon pyrene C₁₆H₁₀ in the external electrostatic field of another pyrene molecule is considered. The calculation showed that the interaction energy of the two-molecule nanocluster increases by a factor of 1.5 if this cluster is in the field of the induced dipole moment of an external pyrene molecule.     

Biography

The mononegative, dinegative and monopositive ions of biphenylene have been formed in solution. The electronic spectra of the negative ions (in tetrahydrofurane and dimethoxyethane solution) have been measured in the range 10 000–44 000 cm^-1, and that of the positive ion (in H₂SO₄ solution) in the range 10 000–35 000 cm^-1. The presence of paramagnetic ions in the solutions of the singly-charged species has been confirmed by measurement of electron spin resonance absorption. The long wavelength electronic spectra of the monopositive and mononegative ions are closely similar, which confirms the essentially ‘aromatic’ character of the biphenylene structure. Assignments are proposed for the principal bands in the spectra of the ions and the neutral molecule. Explicit calculation of the energies of the excited states by an approximate self-consistent field molecular orbital method yields results in reasonably good overall agreement with the experimental energy spectra. There is evidence from relative intensities of some of the bands that the ‘pairing’ of bonding and antibonding sets of molecular orbitals which is characteristic of benzenoid alternant hydrocarbons is partially removed in biphenylene. This may result from a difference of electronegativity of the carbon atoms in the 4-membered ring from that of the remaining carbon atoms.     

Nucleophilic aromatic substitution in chlorinated aromatic systems with a glutathione thiolate model

The conjugation of glutathione with chlorobenzene and di‐, tri‐, tetra‐, and hexa‐chlorinated benzenes via nucleophilic aromatic substitution was modeled for isolated reacting species by ab initio molecular orbital theory to provide an understanding of the intrinsic reactivity of unactivated chloroaromatic systems. Computations at the HF/6‐31+G(d,p) level were augmented with electron correlation corrections using MP2 theory and density functional theory at the B3LYP level. Features of the reaction hypersurface were elaborated using thiolate (thiomethoxide) as the model for an enzyme‐activated glutathione molecule. Unlike the similar reaction with 1‐chloro‐2, 4‐dinitrobenzene a known substrate with glutathione, no σ‐complex or Meisenheimer complex was isolated as a true intermediate on the hypersurface. Instead, the σ‐complex appears as a transition state, preceded and followed by two ion‐molecule complexes in which the approaching and departing anions reside in the plane of the aromatic ring. Solvent calculations show a very similar hypersurface landscape with only one transition state and no intermediate. Activation energies are somewhat greater than for 1‐chloro‐2, 4‐dinitrobenzene owing to the lack of nitro substituents, which provide stabilization in these systems. Nevertheless, activation energies calculated at correlated levels indicate that these reactions are still feasible and consistent with experiment. Transition states and activation energies for dichlorobenzenes and polychlorobenzenes are lower in energy than for chlorobenzene implying greater stability conferred to the transition state by ortho and para substituents.     

New detectors on the basis of copolymer of tetrafluoroethylene with ethylene (PTFE-E)

The registration properties of PTFE-E (F-40, Russia; Tefzel, DuPont, USA; Hostaflon ET, Germany) having exceptional chemical and thermal (about 300°C) resistance are considered. The polymer samples were irradiated with ions in a wide region of masses (from O up to Xe) and energies (from 1 to 6 MeV/amu). Alkaline KMnO₄ solutions at 100°C were used for etching. It is shown that the polymer registration properties depend on the hydrogen content in the polymer. For a copolymer with 2–3 wt% of hydrogen the registration threshold is about 8 MeVcm²/mg. The ion tracks were not found after chemical etching for a copolymer with 1 wt% of hydrogen. Track membranes were produced and examined.     

Positive and negative ion formation via slow electron collisions with 5-bromouridine

Cation and anion formation is studied experimentally upon inelastic low energy electron interactions with 5-bromouridine (BrUrd) using a crossed electron/neutral beams set-up combined with a quadrupole mass spectrometer. The BrUrd molecule belongs to the class of radiosensitizers that increase the sensitivity of DNA (or RNA) to ionizing radiation. In the case of positive ion formation the ionization efficiency curves are measured near the threshold and the corresponding appearance energies are determined using a non-linear least square fitting procedure. The anion yields are investigated in the electron energy range from about 0 to 14 eV. From the comparison of the present results for negative and positive ions information concerning the underlying mechanism of radiosensitizers is deduced.     

Structural,magnetic and electronic properties of single Iron atom at graphene edges

A systemic theoretical study of one iron atom on graphene ribbon edges (Fe/GR) has been carried out by using density functional theory. Thermodynamic stabilities, electronic and magnetic properties of Fe/GR with different edge types and adsorption locations were investigated. According to the Clar's aromatic sextet rule, the formation energies and density of states of Fe atom are found to rely tightly on the ribbon's periodic length. Moreover, Fe atoms on reconstructed zz edges are also stable with low formation energies and semiconducting properties. Finally, the magnetic properties are found sensitive with the structural details, especially the local bond environment. The present theoretical results constitute a useful picture for the deep comprehending on the interface details of the lateral Fe/graphene heterostructures.     

Molecular rotation in liquid crystals selective deuterium spin-lattice relaxation times in the nematic mesophase of 4-cyano-4′-d17-n-octylbiphenyl

The Gibbs ensemble is used to simulate the liquid–liquid equilibria of binary mixtures containing dipolar and non-polar components.The interactions of the dipolar fluid are calculated using the Keesom intermolecular potential. The liquid–liquid coexistence properties are reported for different pressures and different combinations of dipolar/non-polar molecules. The critical properties of the mixtures are estimated. The ability of a dipole to induce phase separation is influenced by the dispersion energy of the molecule. Phase separation is enhanced if the dipolar molecule is also the component with the greatest dispersion energy.     

Low temperature oxidation of benzene and toluene in mixture with n-decane

The oxidation of two blends, benzene/n-decane and toluene/n-decane, was studied in a jet-stirred reactor with gas chromatography analysis (temperatures from 500 to 1100 K, atmospheric pressure, stoichiometric mixtures). The studied hydrocarbon mixtures contained 75% of aromatics in order to highlight the chemistry of the low-temperature oxidation of these two aromatic compounds which have a very low reactivity compared to large alkanes. The difference of behavior between the two aromatic reactants is highly pronounced concerning the formation of derived aromatic products below 800 K. In the case of benzene, only phenol could be quantified. In the case of toluene, significant amounts of benzaldehyde, benzene, and cresols were also formed, as well as several heavy aromatic products such as bibenzyl, phenylbenzylether, methylphenylbenzylether, and ethylphenylphenol. A comparison with results obtained with neat n-decane showed that the reactivity of the alkane is inhibited by the presence of benzene and, to a larger extent, toluene. An improved model for the oxidation of toluene was developed based on recent theoretical studies of the elementary steps involved in the low-temperature chemistry of this molecule. Simulations using this model were successfully compared with the obtained experimental results.