Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2−) Collisions with Benzene (C6H6) Molecules

In this study, novel experimental total electron detachment cross sections for O₂⁻ collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 (u) cations formation, which contributed to the broad local maximum in the total ionisation observed from 550 to 800 eV. This work reveals the reactivity induced by molecular anions colliding with hydrocarbons at high energies, processes that can take place in the interstellar medium under various local conditions.     

High field conduction in poly(p-phenylene vinylene)

We have shown that in polyacetylene, for electric fields above 10⁶ V/cm polarons are dissociated because the electron or hole can move much faster than the lattice distortion. Similar results should hold for poly(p-phenylene vinylene), PPV. To determine whether the free carriers thus created can be heated by the field sufficiently to allow impact ionization, we investigated free-carrier scattering in PPV. The important scatterers are longitudinal acoustic modes, molecular vibrations, and librational torsional modes. The coupling constants and important frequencies are known approximately for the first two of these processes in PPV. Using these values, some reasonable values for librons, and the calculated band structure of PPV, we conclude that at least some of the carriers could be heated to 2 eV at a field of ∼10⁶ V/cm, and that they could acquire energy required for impact ionization at not much higher fields.     

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.     

Photoelectron Spectroscopy of OH−-Anion–Water Clusters Generated by Ultrasonic Nebulizer

Investigating molecules in the gas phase is the only way to discover their intrinsic molecular properties; however, it is challenging to produce the gaseous phase of large-molecule chemicals. Thermal evaporation is typically used to convert molecules into gases, but it is still challenging to study ionic molecules in solutions in the gas phase. Electrospray ionization is one of the best methods to generate molecules in the gas phase, and it is uniquely capable of studying large biomolecules, including proteins. However, the molecular temperature required to study the spectroscopic properties of the molecules is very high. In this study, we developed a new, simple evaporation method using an ultrasonic nebulizer to obtain gas-phase molecules. Using this new equipment, we observed OH⁻ anions and their water clusters in the gas phase and obtained their photoelectron spectra. We observed that the vertical electron-detachment energy (VDE) of OH⁻ was 1.90 ± 0.05 eV and the VDEs of its water clusters and OH⁻ (H₂O)_n (n = 1–2) decreased to 1.50 ± 0.05 eV (n = 1) and 1.30 ± 0.05 eV (n = 2), respectively.     

Irradiation effects on electrical properties of cellulose nitrate

Cellulose nitrate (CA-80-15) films were exposed to UV and neutron irradiations. An increase of the electrical conductivity was observed. The values of the activation energy diminish with irradiation from 0.42 to 0.15 eV for UV and to 0.31 eV for neutron irradiation. A sharp increase in the current was observed after exposing CA-80-15 samples to fission neutron fluences of 1*10⁷ n/cm². The electrical conduction in cellulose nitrate is governed by the Shottky mechanism. The value of the electron affinity of the polymer used is 4.46 eV. This value is increased after both types of irradiation. The dielectric permittivity (ε′) of the above samples together with the dielectric loss factor (ε″) were measured over a range of temperatures (293–403 K) at fixed frequencies (1*10³, 1*10⁴, and 1*10⁵Hz). Three neutron exposures (? = 1*10⁵, 1*10⁶, and 1*10⁷ n/cm²) were used. The obtained results made it possible to determine a complete set of conduction parameters including dielectric susceptibility χ, ac conductivity α_ac, and temperature coefficient of permittivity TC. © 1995 John Wiley & Sons, Inc.     

Study of Jet-Cooled Bis(η6-Benzene)Chromium by Multiphoton Zero Kinetic Energy—Mass-Analyzed Threshold Ionization Spectroscopy

Zero kinetic energy-mass-analyzed threshold ionization (ZEKE-MATI) spectra of jet-cooled (η⁶-C₆H₆)₂Cr have been obtained for the first time with use of the 3d_z2 → R4p_x,y Rydberg transition as the initial step of the electronic excitation. The ionization potential of (η⁶-C₆H₆)₂Cr determined on the basis of the ZEKE-MATI experiment is 44087 ± 3 cm⁻¹ (5.4661 ± 0.0004 eV). The binding energy of the R4p_x,y electron is 17333 ± 3 cm⁻¹. The frequencies of the symmetric metal-ring stretching vibration and CH umbrella vibration in the gas-phase ground-state molecular cation (η⁶-C₆H₆)₂Cr⁺ are 262 ± 5 and 788 ± 4 cm⁻¹, respectively.     

Admittance spectroscopy of a phosphorus-doped n-diamond homoepitaxial layer

Generation and recombination processes of electrons through phosphorus (P) donor are analyzed by admittance spectroscopy for a Ni/Au Schottky contact on an n-diamond epilayer. The dependence of capacitance and conductance frequency on temperature is interpreted by Shockley–Read–Hall statistics. The thermal ionization energy and capture cross-section of P donor are evaluated to be 0.54 ± 0.02 eV and (4.5 ± 2.0) × 10^{− 17} cm², respectively. Broadening of the conductance–frequency curve is observed, which is believed to be evidence of a long Debye tail of electron distribution at the depletion layer edge.     

Electron-Induced Decomposition of Uracil-5-yl O-(N,N-dimethylsulfamate): Role of Methylation in Molecular Stability

The incorporation of modified uracil derivatives into DNA leads to the formation of radical species that induce DNA damage. Molecules of this class have been suggested as radiosensitizers and are still under investigation. In this study, we present the results of dissociative electron attachment to uracil-5-yl O-(N,N-dimethylsulfamate) in the gas phase. We observed the formation of 10 fragment anions in the studied range of electron energies from 0–12 eV. Most of the anions were predominantly formed at the electron energy of about 0 eV. The fragmentation paths were analogous to those observed in uracil-5-yl O-sulfamate, i.e., the methylation did not affect certain bond cleavages (O-C, S-O and S-N), although relative intensities differed. The experimental results are supported by quantum chemical calculations performed at the M06-2X/aug-cc-pVTZ level of theory. Furthermore, a resonance stabilization method was used to theoretically predict the resonance positions of the fragment anions O⁻ and CH₃⁻.     

Surface energy and adsorption energy distribution measurements on some carbon blacks

The dispersive component of the surface energy (γ_s^d) of various carbon blacks and of nitric acid or heat-treated samples has been measured by inverse gas chromatography (IGC). It is shown that IGC, at infinite dilution, applies poorly to carbon blacks and provides only apparent and excessively high values of γ_s^d (a few hundreds of mJ/m²). IGC, at finite concentration, readily allows the obtention of n-alkanes, benzene and chloroform adsorption isotherms from which various thermodynamic values are computed (spreading pressure π, isosteric enthalpy of adsorption, surface energy characteristics). The γ_s^d values calculated from π_e are in the 80–120 mJ/m² range (i.e. values which are in fair agreement with published data on graphite or graphitized carbons). Further, the specific interaction potential of polar probes is in relation, as expected, with the oxygen content of the carbons. Finally, from the adsorption isotherms, the adsorption energy distribution function is computed, supposing a patchwise distribution of adsorption sites. The results confirm the high surface heterogeneity of carbon blacks and the influence of surface treatments, but indicate also major differences between carbon blacks from different preparation processes.     

Optical Energy Estimation of Irradiated Polypropylene

The optical absorption has been studied under exposure to gamma radiation. Thin films of polypropylene were irradiated with a ⁶⁰Co source and doses ranged up to 6 kGy. Analysis of the optical absorption spectra indicated that both direct and indirect electron transitions take place in the polymer. The observed optical energy gap (E_opt) and energy gap-tail (ΔE) for irradiated films were determined from the measured absorption spectra. The average values of (E_opt) and (ΔE) are 5.85 eV and 0.5 eV, respectively. There is no detectable change in the optical energy gaps and tails under the applied gamma-ray doses.     

Acceptor formation in Mg-doped,indium-rich GaxIn1?xN: evidence for p-type conductivity

We report on the Mg-doped, indium-rich Ga_xIn_1−xN (x < 30). In the undoped material, the intrinsic electron density is very high and as a result there is no detectable photoconductivity (PC) signal within the range of temperatures of 30 <T < 300 K. In the Mg-doped material however, where the conductivity is reduced, there is a strong PC spectrum with two prominent low-energy peaks at 0.65 and 1.0 eV and one broad high-energy peak at around 1.35 eV. The temperature dependence of the spectral photoconductivity under constant illumination intensity, at T > 150 K, is determined by the longitudinal-optical phonon scattering together with the thermal regeneration of non-equilibrium minority carriers from traps with an average depth of 103 ± 15 meV. This value is close to the Mg binding energy in GaInN. The complementary measurements of transient photoluminescence at liquid He temperatures give the e-A⁰ binding energy of approximately 100 meV. Furthermore, Hall measurements in the Mg-doped material also indicate an activated behaviour with an acceptor binding energy of 108 ± 20 meV.     

Thermal and chemical ionization in flames

Conclusions We have determined the rate constants of the potassium ionization process AA⁺+e^– in the flames of 2H₂+O₂+X (Ar, He) mixtures on the temperature interval 1500–2500° K. The activation energy of this process is close to the ionization potential of potassium (100 kcal).In our experiments the rate of ion formation in the front of a hydrogen flame seeded with potassium exceeded the purely thermal ionization rate by 0.5–2 orders. The presumed cause is recombination ionization of the potassium in the flame front, for example, K+O+OK⁺+O₂+e^–. This is confirmed by the intensification of ionization in the reaction zone in the presence of an excess of oxygen in homogeneous H₂-air and H₂–O₂–(He, Ar) mixtures with alkali impurities.At T=1700° K the recombination coefficient for electrons and potassium ions is close to 1·10^–8 cm³·sec^–1. For a more precise determination it is necessary to know the frequency of electron capture by molecules and atoms under the experimental conditions.Experiments on thermal ionization in turbulent flames confirm the earlier conclusion concerning the important role of mass transfer in the chemi-ionization of hydrocarbon flames.Fizika Goreniya i Vzryva, Vol. 6, No. 1, pp. 37–48, 1970     

A New Perspective on Adsorbent Materials Based Impregnated MgSiO3 with Crown Ethers for Palladium Recovery

The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO₃-DB30C10 have a higher adsorption capacity (35.68 mg g⁻¹) compared to MgSiO₃-DB18C6 (21.65 mg g⁻¹). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS⁰) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.     

Determination of secondary transitions and thermodynamic interaction parameters of poly (ether imide) by inverse gas chromatography

Summary The retention diagrams of poly(ether imide) for ethyl benzene, n-propyl benzene, isopropyl benzene, chloro benzene, n-butyl acetate, tert-butyl acetate, isoamyl acetate, n-nonane, n-decane, n-undecane, n-dodecane and n-tridecane were obtained by inverse gas chromatography technique. In this work, the slope changes on the diagram were assigned as secondary transitions. The secondary transition temperatures obtained by inverse gas chromatography technique are in good agreement with the ones obtained by thermally stimulated depolarization current in the literature. Specific retention volume, V_g⁰, the weight fraction activity coefficients of the solvents at infinite solution, Ω₁^∞, Flory-Huggins polymer-solvent interaction parameters,χ₁₂^∞, equation-of-state polymer-solvent interaction parameters,χ₁₂^*, effective exchange energy parameters, X_eff were determined. Later, the partial molar heat of sorption, and the partial molar heat of mixing, were obtained. The solubility parameter of poly(ether imide), δ₂ was determined as 10.7 (cal/cm³)^1/2 by extrapolation of the δ₂ values obtained by considering the free volume effects from studied temperature range to room temperature.     

Catalytic properties of Ru-η-C6H6-diphosphine complexes for hydrogenation of benzene in aqueous-organic biphasic system

The influences of pH on the catalytic properties of Ru-η⁶-C₆H₆-diphosphine complex [RuCl(η⁶-C₆H₆)(BISBI)]Cl (1) (BISBI = 2,2′-bis(diphenylphosphinomethyl)-1,1′-biphenyl), [RuCl(η⁶-C₆H₆)(BDPX)]Cl (2) (BDPX = 1,2-bis(diphenylphosphinomethyl)benzene), Ru₂Cl₄(η⁶-C₆H₆)₂(μ₂-BDNA) (3) (BDNA = 1,8-bis(diphenylphosphinomethyl)naphthalene), [RuCl(η⁶-C₆H₆)(BISBI)]BF₄ (4), [RuCl(η⁶-C₆H₆)(BDPX)]BF₄ (5), and [(η⁶-C₆H₆)₂Ru₂Cl₂(μ₂-Cl)(μ₂-BDNA)]BF₄ (6) for the hydrogenation of benzene were investigated in aqueous-organic biphasic system. The hydrogenation of benzene catalyzed by all complexes yielded only cyclohexane. The catalytic results revealed that the stabilities of these complexes were not only closely relative with their compositions or molecular structures but also the pH value of aqueous solution. Complexes 1 and 2 were homogeneous catalysts at pH <5, but complexes 3, 4, 5 and 6 were partly decomposed in the same reaction conditions and played simultaneously the roles of homogeneous and heterogeneous catalysts. When the pH was up to 12, all of six complexes were gradually decomposed to Ru(0) particles. The addition of extra phosphine ligand was favorable to prevent these complexes from decomposing in the catalytic process. The experiment of mercury poisoning and the curve of conversion vs time strongly supported above conclusions.     

PLG-007 and Its Active Component Galactomannan-α Competitively Inhibit Enzymes That Hydrolyze Glucose Polymers

PLG-007 is a developmental therapeutic compound that has been clinically shown to reduce the magnitude of postprandial glucose excursions and has the potential to be an adjunct treatment for diabetes and inflammatory-related diseases. The present investigation is aimed at understanding the molecular mechanism of action of PLG-007 and its galactomannan (GM) components GMα and GMβ (in a 1:4 mass ratio, respectively) on enzyme (i.e., α-amylase, maltase, and lactase) hydrolysis of glucose polymers using colorimetric assays and ¹³C HSQC NMR spectroscopy. The starch–iodine colorimetric assay indicated that GMα strongly inhibits α-amylase activity (~16-fold more potent than GMβ) and thus is the primary active component in PLG-007. ¹³C HSQC experiments, used to follow the α-amylase-mediated hydrolysis of starch and amylopectin, further demonstrate the α-amylase inhibitory effect of GMα via α-amylase-mediated hydrolysis of starch and amylopectin. Maltohexaose (MT6) was used to circumvent the relative kinetic complexity of starch/amylopectin degradation in Michaelis–Menten analyses. The V_max, K_M, and K_i parameters were determined using peak volume integrals from ¹³C HSQC NMR spectra. In the presence of PLG-007 with α-amylase and MT6, the increase in K_M from 7.5 ± 0.6 × 10⁻³ M (control) to 21 ± 1.4 × 10⁻³ M, with no significant change in V_max, indicates that PLG-007 is a competitive inhibitor of α-amylase. Using K_M values, K_i was estimated to be 2.1 ± 0.9 × 10⁻⁶ M; however, the microscopic K_i value of GMα is expected to be larger as the binding stoichiometry is likely to be greater than 1:1. Colorimetric assays also demonstrated that GMα is a competitive inhibitor of the enzymes maltase and lactase. Overall, this study provides insight as to how PLG-007 (GMα) is likely to function in vivo.     

Band alignment and enhanced breakdown field of simultaneously oxidized and nitrided Zr film on Si

The band alignment of ZrO₂/interfacial layer/Si structure fabricated by simultaneous oxidation and nitridation of sputtered Zr on Si in N₂O at 700°C for different durations has been established by using X-ray photoelectron spectroscopy. Valence band offset of ZrO₂/Si was found to be 4.75 eV, while the highest corresponding conduction offset of ZrO₂/interfacial layer was found to be 3.40 eV; owing to the combination of relatively larger bandgaps, it enhanced electrical breakdown field to 13.6 MV/cm at 10^-6 A/cm².     

Synthesis and properties of 2-(10,11-dihydrodibenz[b,f]azepine-5-yl)carbazole-based monomers and polymers

The synthesis of a series of 2-(10,11-dihydrodibenz(b,f)azepinyl)carbazole-based monomers is reported. Full characterization of their structures is presented. The monomers were subjected to cationic polymerization using BF₃·O(C₂H₅)₂ as an initiator. The synthesized monomers and polymers were examined by differential scanning calorimetry, UV spectrometry, cyclic voltammetry and electron photoemission spectrometry. The electrochemical investigation of the solutions of the synthesized compounds revealed HOMO values ranging from −5.12 to −5.06 eV. Electron photoemission spectrometry of the solid samples gave ionization potentials of 5.40–5.50 eV.     

Catalytic hydrogenation of benzene to cyclohexene on Ru(0 0 0 1) from density functional theory investigations

The catalytic hydrogenation of benzene on transition metal surfaces is of fundamental importance in petroleum industry. With the aim to improve its efficiency and particularly the selectivity to cyclohexene, in this contribution we perform periodic density functional theory calculations to determine the potential energy surface in the hydrogenation of benzene on Ru(0 0 0 1). By following the Horiuti–Polanyi mechanism with a step-wise addition of hydrogen adatoms, we investigate the adsorption of all the possible reaction intermediates and identify the most favored adsorption configuration for each intermediate. In particular, the most stable isomer for the same C₆H_n (n = 8, 9, 10) species are revealed as the most conjugated isomers, which are consistent with those in the gas phase. The elementary hydrogenation reactions of the most stable intermediates are then investigated under different H coverage conditions: the reaction barriers are calculated to be 0.68–0.97 eV at the low H coverage and 0.32–1.14 eV at the high H coverage. The high H coverage reduces significantly the overall barrier height of hydrogenation. With the determined pathway, we propose that the hydrogenation of benzene on Ru(0 0 0 1) follows the mechanism with the step-wise hydrogenation of neighboring C atoms in the ring, i.e., 1–2–3… hydrogenation. The selectivity to cyclohexene on Ru is also discussed, which highlights the importance of the π mode adsorption of benzene and also the adverse effect of secondary reaction process involving the readsorption and hydrogenation of cyclohexene.     

Solution processable C60 fullerene-hydrazone dyads for optoelectronics

Ambipolar, narrow band gap (∼1.35 eV) fullerene-arylhydrazone dyads have been synthesized utilizing the Prato-Maggini-Scorrano reaction followed by the condensation with phenylhydrazines. Room temperature electron and hole mobilities, measured by the xerographic time of flight technique, exceed 10⁻⁴ cm² V⁻¹ s⁻¹ at strong electric fields. The values of ionization potential, measured by the photoemission in air method, are in the range of 5.29–5.36 eV. Good ambipolar charge transport, photosensitivity across the whole visible light region of the spectrum, and solubility in common organic solvents makes these dyads attractive materials for various optoelectronic applications.