The standard enthalpy of formation of fullerene chloride C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>

A rotating-bomb calorimeter was used to measure the energy of combustion of crystalline fullerene chloride C₆₀Cl₃₀ · 0.09Cl₂, Δ_c U° = (?24474 ± 135 kJ/mol). The result was used to calculate the standard enthalpy of formation, Δ_f H° (C₆₀Cl₃₀, cr) = 135 ± 135 kJ/mol, and the C-Cl bond energy, 195 ± 5 kJ/mol. The C-X (X = F, F, Cl, and Br) bond energies in fullerene C₆₀ derivatives and other organic compounds are compared.     

Relationship between spontaneous generation of voltage and structural features in a single crystal of Pr0.6Ca0.4MnO3

Spontaneous generation of electrical voltage U was found for the perovskite-like single crystal of Pr_0.6Ca_0.4MnO₃, wherein the charge and orbital orderings occur at T _CO = 240 K and the antiferromagnetic one occurs at the Neel point T _N = 174 K. With decreasing the temperature, the U value increases first slowly (in the temperature range of 300 K-T _CO) and then more rapidly (T _CO-T _N). Starting from T _N, U increases exponentially and, at 85 K, reaches the value of 115 mV (in the ab plane) and 6.5 mV (along the c axis). The magnetic field has a different effect on the U value in different temperature ranges: in the temperature range of 85–130 K, it decreases U and, in the range of 130–240 K, increases U. The spontaneous voltage is thought to be caused by the existence of ferromagnetic and charge-orbital-ordered clusters of different topology in the sample. The latter clusters have own features and their structure are described by the non-centrosymmetric space group P2₁ nm.     

Comparison of thermal curing behavior of liquid and solid urea–formaldehyde resins with different formaldehyde/urea mole ratios

This study was undertaken to compare thermal cure kinetics of urea–formaldehyde (UF) resins, in both liquid and solid forms as a function of formaldehyde/urea (F/U) mole ratio, using multi-heating rate methods of differential scanning calorimetry. The requirement of peak temperature (T _p), heat of reaction (ΔH) and activation energy (E) for the cure of four F/U mole ratio UF resins (1.6, 1.4, 1.2 and 1.0) was investigated. Both types of UF resins showed a single T _p, which ranged from 75 to 118 °C for liquid resins, and from 240 to 275 °C for solid resins. As the F/U mole ratio decreased, T _p values increased for both liquid and solid resins. ΔH values of solid resins were much greater than those of liquid resins, indicating a greater energy requirement for the cure of solid resins. The ΔH value of liquid UF resins increased with decreasing in F/U mole ratio whereas it was opposite for solid resins, with much variation. The activation energy (E _a) values calculated by Kissinger method were greater for solid UF resins than for liquid resins. The activation energy (E _α ) values calculated by isoconversional method which showed that UF resins in liquid or solid state at F/U mole ratio of 1.6 followed a multi-step reaction in their cure kinetics. These results demonstrated that thermal curing behavior of solid UF resin differed greatly from that of liquid resins, because of a greater branched network structure in the former.     

Dissociative photoionization of isoprene: experiments and calculations

Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C₅H₇⁺, C₅H₅⁺, C₄H₅⁺, C₃H₆⁺, C₃H₅⁺, C₃H₄⁺, C₃H₃⁺ and C₂H₃⁺ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C₅H₈ and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C₅H₈, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C₅H₈. Copyright © 2009 John Wiley & Sons, Ltd.     

Lattice energies of the alkali metal bifluorides, U(MHF2)

The experimental determination of the hydrogen bond energy of the bifluoride ion makes possible accurate lattice energies of the alkali metal bifluorides, U(MHF₂); see Table 1. From these it is possible to estimate those of NH₄HF₂ and the alkaline earth bifluorides.     

The self‐consistent charge density functional tight‐binding theory study of carbon adatoms using tuned Hubbard U parameters

The self‐consistent charge density functional tight‐binding (DFTB) theory is a useful tool for realizing the electronic structures of large molecular complex systems. In this study, the electronic structure of C₆₁ formed by fullerene C₆₀ with a carbon adatom is analyzed, using the fully localized limit and pseudo self‐interaction correction methods of DFTB to adjust the Hubbard U parameter (DFTB + U). The results show that both the methods used to adjust U can significantly reduce the molecular orbital energy of occupied states localized on the defect carbon atom and improve the gap between highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) of C₆₁. This work will provide a methodological reference point for future DFTB calculations of the electronic structures of carbon materials.     

The influence of an electric field on the wetting of an SiO2 film by ionic liquids

The electrowetting of a dielectric SiO₂ film 100 nm thick by drops (D = 2–3 mm) of [C₄mIm][PF₆], [C₆mIm][PF₆], and [C₆mIm][BTI] ionic liquids was studied at |U| ≤ 60 V in a ～10^?8 mbar vacuum. Electrocapillary curves of the dependence of the wetting angle on electric field potential were constructed with an accuracy of ±1 deg. In conformity with the Young-Lippman equation, the wetting angle θ° decreased by the parabolic law from 51° to 43° for [C₄mIm][PF₆], from 48° to 38° for [C₆mIm][PF₆], and from 35° to 27° for [C₆mIm][BTI] as |U| increased at 298 K. The electrocapillary curve branches were situated symmetrically in the (θ°, U) coordinates with respect to the line passing through the point U = 0; that is, zero-charge potential is zero for the electrowetting of the dielectric film by the ionic liquids. The capacitance of the double electrical layer at the ionic liquid-dielectric interface was determined. This value was found to be 4.65, 2.93, and 1.73 μF/m² for the electrowetting of the SiO₂ film at 298 K by the ionic liquids specified, respectively.     

Internal excitation effects in the photodissociation of size selected ethylene and methanol dimers

The infrared photodissociation spectra of C₂H₄ and CH₃OH dimers are measured for different internal excitation energies ΔE. The dimers are size-selected in a scattering process with He and the internal energy is varied by using (1) different collision energies, (2) different scattering angles and (3) by measuring the complete energy loss spectra with and without laser radiation by time-of-flight analysis of the scattered clusters. For (CH₃OH)₂ the width Γ of the spectrum increases strongly with ΔE, while the cross section at the maximum is constant, a normal behaviour for an inhomogeneously broadened system. For (C₂H₄)₂ Γ is nearly constant after a sort of threshold and the cross section increases with increasing ΔE. These results are explained by hot band excitation and the coupling to the darkv ₁₀-mode.     

Determination of combustion energies and the standard enthalpies of formation for the complexes of RE(Et<Subscript>2</Subscript>dtc)<Subscript>3</Subscript>(phen)

Solid complexes, RE(Et₂dtc)₃(phen) (RE=La, Pr, Nd, Sm—Lu), were synthesized with sodium diethyldithiocarbamate (NaEt₂dtc3H₂O), 1,10-phenanthroline (o-phen?H₂O) and hydrated lanthanide chlorides in absolute ethanol. The constant-volume combustion energies of complexes, Δ _C U, were determined by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion, Δ_CH_m ^θ, and standard enthalpies of formation, Δ_fH_m ^θ, were calculated for these complexes, respectively. The experiment results showed the “tripartite effect” of rare earth.     

Dynamic computer simulations of Cs incorporation in Si during low‐energy (0.2–3 keV) irradiation

The incorporation of Cs atoms in silicon was investigated by dynamic computer simulations using the Monte‐Carlo code T‐DYN that takes into account the gradual change of the target composition due to the Cs irradiation. The implantation of Cs atoms at normal incidence was studied for four energies (0.2, 0.5, 1, and 3 keV) and three different Cs surface‐binding energies U_Cs (0.4, 0.8, and 2.4 eV). The total implantation fluences were 2 × 10¹⁷ Cs cm^?2 for 0.2 keV, 1.5 × 10¹⁷ Cs cm^?2 for 0.5 keV, and 1 × 10¹⁷ Cs cm^?2 for 1 and 3 keV. At these values, a stationary state has been reached. The steady‐state Cs‐surface concentrations exhibit a pronounced dependence both on impact energy and U_Cs, varying between ～1 (at 0.2 keV and U_Cs = 2.4 eV) and ～0.13 (3 keV and U_Cs = 0.4 eV). Under equilibrium, the partial sputtering yield of Si, Y_Si, experiences little influence of U_Cs, but varies with the Cs energy: at U_Cs = 0.8 eV from 0.09 to 1.0 Si atoms/Cs projectile. For all irradiation conditions a strongly preferential sputtering of Cs atoms as compared to Si atoms is found, increasing from 1.8 (at 3 keV and U_Cs = 2.4 eV) to 13.3 (at 0.2 keV and U_Cs = 0.4 eV). Preferential sputtering of Cs increases with decreasing irradiation energy and decreasing U_Cs. Copyright © 2008 John Wiley & Sons, Ltd.     

A united-residue force field for off-lattice protein-structure simulations. II. Parameterization of short-range interactions and determination of weights of energy terms by Z-score optimization

Continuing our work on the determination of an off-lattice united-residue force field for protein-structure simulations, we determined and parameterized appropriate functional forms for the local-interaction terms, corresponding to the rotation about the virtual bonds (U_tor), the bending of virtual-bond angles (U_b), and the energy of different rotameric states of side chains (U_rot). These terms were determined by applying the Boltzmann principle to the distributions of virtual-bond torsional and virtual-bond angles and side-chain rotameric states, respectively, calculated from a data base of 195 high-resolution nonhomologous proteins. The complete energy function was constructed by combining the individual energy terms with appropriate weights. The weights were determined by optimizing the so-called Z-score value (which is the normalized difference between the energy of the native structure and the mean energy of non-native structures) of the histidine-containing phosphocarrier protein from Streptococcus faecalis (1PTF; an 88-residue α + β protein). To accomplish this, a database of C^α patterns was created using high-resolution nonhomologous protein structures from the Protein Data Bank, and the distributions of energy components of 1PTF were obtained by threading its sequence through ∼500 randomly chosen C^α-patterns from the X-ray structures in the PDB, followed by energy minimization, with the energy function incorporating initially guessed weights. The resulting minimized energies were used to optimize the Z-score value of 1PTF as a function of the weights of the various energy terms, and the new weights were used to generate new energy-component distributions. The process was iterated, until the weights used to generate the distributions and the optimized weights were self-consistent. The potential function with the weights of the various energy terms obtained by optimizing the Z-score value for 1PTF was found to locate the native structures of other test proteins (within an average RMS deviation of 3 Å): calcium-binding protein (4ICB), ubiquitin (1UBQ), α-spectrin (1SHG), major cold-shock protein (1MJC), and cytochrome b₅ (3B5C) (which included α and β structures) as distinctively lowest in energy in similar threading experiments. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 874–887, 1997     

Comparison of Gasoline-Ranged <Emphasis Type="Italic">n</Emphasis>-Alkanes Conversions Using Dielectric Barrier Discharge: A Kinetic Study

Here, we compared the conversion of gasoline-ranged n-alkanes (C₆–C₉) using dielectric barrier discharge. For an energy density of ~68 J/L and an initial n-alkane concentration of ~230 ppm, when carbon number increased from 6 to 9, the energy efficiency of n-alkane conversion increased from 117 to 240 mmol/kWh, CO _x selectivity decreased from 46 to 20%, and ozone concentration increased from 216 to 240 ppm. The effect of energy density and initial n-alkane concentration were also investigated. The understanding of initial step of conversion was greatly aided by a proposed kinetic model. The pathways of consecutive reactions from the initiation to products were also discussed.     

Thermodynamics of the URuC system

Thermodynamic measurements by the electromotive force method were made on the binary intermetallic phases URu₃ and U₃Ru₅ and on the ternary carbides URu₃C_0.7 and U₂RuC₂ of the URu and the URuC systems between 950 and 1200 K using galvanic cells with CaF₂ single crystal electrolytes: U, UF₃¦CaF₂¦UF₃, URu₃, Ru; U, UF₃¦CaF₂¦UF₃, U₃Ru₅, URu₃; Ru, URu₃, UF₃¦CaF₂¦UF₃, URu₃C_0.7, Ru, C; U, UF₃¦CaF₂¦UF₃, URu₃C_0.7, U₂RuC₂, C. The Gibbs energies of formation of URu₃, U₃Ru₅, URu₃C_0.7 and U₂RuC₂ were evaluated from the measured electromotive force which give ^fΔG^o〈URu₃〉 = −199 100 + 35.9 T J mol^−1fΔG^o〈U₃Ru₅〉 = −398 600 + 43.6 T J mol^−1fΔG^o〈URu₃C_0.7〉 = −192 600 + 2.5 T J mol^−1fΔG^o〈U₂RuC₂〉 = −380 200 + 52.5 T J mol⁻¹ The implications of these thermodynamic data for the behaviour of the fission product ruthenium in irradiated carbide fuels are discussed.     

An experimentally based description of the ground-state wavefunction for two weakly coupled electrons by photoelectron spectroscopy and magnetic susceptibility measurements

It is possible to extract values for the transfer energy, t, and the Coulomb interaction, U, in hydrogen-like systems from a combination of photoelectron and magnetic data, as both the form of the photoelectron spectrum and the exchange splitting are determined by these quantities. This procedure is used to evaluate the ground-state wavefunction for the two weakly coupled Ti 3d electrons in (C₁₀H₈)(C₅H₅)₂Ti₂Cl₂.     

The nonsinglet instabilities of the hartree-fock solutions for nonalternant hydrocarbons

The nonsinglet instabilities of the restricted Hartree-Fock (RHF) solutions for the nonalternant hydrocarbons, propalene, pentalene, heptalene and nonalene, that have been known to show the lattice instabilities (bond-length alternations) when treated within a semiempirical RHF approximation are examined. By examining the energy lowerings due to the appearance of the spin-density-wave (SDW) solutions, or better, of the singlet projected SDW solutions, we show that the treatment of the lattice instability based on the RHF theory is valid at least in these molecules. On the basis of the energy lowerings E(E _RHF-E _SDW), we discuss-the dependence of the electron correlation energies on the number of -electrons.     

Electronic transitions in C60 and its ions

The electronic spectrum of C₆₀ is calculated using quantum mechanical methods. The first allowed transition in C₆₀ is calculated at an energy of 3.5 eV and with an oscillator strength of 0.09. Several transitions are found at higher energies with comparatively strong oscillator strengths, the strongest one being at 5.78 eV (λ=214 nm). The calculated energy level diagram of C₆₀ is also used to predict wavelengths for transitions in C ₆₀ ⁺ and C ₆₀ ^? . A comparison is made with some recently observed diffuse interstellar bands at 1180 nm and 1320 nm, which have been speculated to originate from C ₆₀ ⁺ .     

Estimation of the heat capacity of some uranium-rare earth mixed oxides from thermal expansion and vice versa

Estimation of the high temperature heat capacity (C _p) data from experimental high temperature thermal expansion (α _v) data and vice versa from the known values of the ratio (α_v/C _p) at low temperatures were carried out by assuming linear relationship of the ratio α _v /C _p with temperature (at T > θ _D). The assumption was examined using the known α _v and C _p values of single phase fluorite systems such as UO₂, ThO₂ and PuO₂. It was also examined using the known α _v and C _p of the mixed oxides (U_1?y La_y) O_2±x (y = 0.2, 0.4, 0.6 and 0.8). The estimated values of α _v and C _p are in good agreement with the experimental values within ±3%. Using the assumption the high temperature heat capacity data of (U_1?y Ce _y ) O₂ (y = 0.2, 0.8) and (U_1?y Gd _y ) O_2±x (y = 0.2, 0.5) were computed from the experimental high temperature α _v data.     

The crystal structure of U5Re3C8

U₅Re₃C₈ crystallizes tetragonal in space group P4/mbm with the lattice constantsa=1 131.3(1) pm,c=330.29(7) pm,V=0.4227 nm³ andZ=2 formula units per cell. The structure was determined from single-crystal counter-data and refined to a residual ofR=0.032 for 649 structure factors and 24 variable parameters. It is of a new type with carbon atoms on three different sites with approximately octahedral environment of five uranium and one rhenium or four uranium and two rhenium atoms. The positions of the metal atoms correspond to those of a (slightly distorted) cubic body centered structure as is also found for Ho₂Cr₂C₃, UCr₄C₄, UMoC₂, YCoC, and U₂IrC₂.     

Unimolecular decomposition of energy-selected anisole ions. Breakdown graph and metastable decay rates

The fragmentation behavior of the anisole ion (C₆H₅OCH^+·₃) was examined using threshold photoelectron-photoion coincident (TPEPICO) mass spectrometry. Four major fragments are observed in the ion time-of-flight spectra at photon energies less than 14 eV: C₆H₅O⁺ (m/z 93), C₆H⁺₇ (m/z 79), C₆H⁺₆ (m/z 78), and C₅H⁺₅ (m/z 65). Rate constants for the production of the ion m/z 78 near threshold were found to agree well with those calculated on the basis of RRKM theory. Most of the excess energy at threshold for this process is a result of the kinetic shift.