Theoretical determination of the ionization potentials of the 1σ and 2σ electrons of CO(Σ)

Large-basis-set calculations of near Hartree-Fock accuracy were performed on CO⁺(1σ-hole ²Σ⁺) and CO⁺)2σ-hole, ²Σ⁺); correlation energies for these systems and for CO were calculated using an atoms-in-molecule approach, relativistic energies and vibrational structure corrections were also considered. The results are: IP(CO, 1σ) = 542.4 (542.57) eV, IP(CO,2σ) = 297.0 (296.24) cV, D_c(CO, ¹Σ⁺) = 10.8 (11.1) Ev, D₃(CO⁺, 1σ, ²Σ⁺) = 11.9 eV, D_e(CO⁺, 2σ, ²Σ⁺) = 9.1 eV, where IP and D_e stand respectively for ionization potential and dissociation energy, and where the numbers in parentheses refer to the most recent experimental values. The electron transfers resulting from the ionization of inner-shell electrons are discussed. Finally a quantitative correlation is developed correlating absolute chemical shifts to charge densities. Agreement between the calculated values and those derived from the correlation is quite satisfactory.     

A quantum mechanical study of the decomposition of CF3OCF3 and CF3CF2OCF2CF3 in the presence of AlF3

The effect of AlF3 on the decomposition of CF3OCF3 and CF3CF2OCF2CF3 is investigated using ab initio theory. Previous work by Pancansky et al. [Pacansky, J.; Waltman, R. J. J Fluorine Chem. 1997, 83, 41] showed that AlF3 significantly reduces the activation energy of the decomposition of CF3OCF3 due to the strong electrostatic interaction between the aluminum trifluoride and the reactant. In this work, a new transition-state structure and reaction mechanism have been identified for the decomposition of CF3OCF3 in the presence of AlF3. This new mechanism shows that AlF3 functions by accepting a fluorine atom from one carbon and simultaneously donating a fluorine atom to the other carbon. We show that the same pathway is obtained independently of the level of theory. The reaction rate, generated via statistical mechanics and transition-state theory, is 2-3 orders of magnitude higher for the new transition state when compared to that of the old one. The study was also performed for CF3CF2OCF2CF3 in order to ascertain the effect of chain length on the reaction mechanism and rate. We find that an analogous transition state, with lower activation energy, provides the lowest-energy path for decomposition of the longer chain.     

Understanding the rate of spin-forbidden thermolysis of HN3 and CH3N3

The pyrolysis of the simplest azides HN(3) and CH(3)N(3) has been studied computationally. Nitrogen extrusion leads to the production of NH or CH(3)N. The azides have singlet ground states but the nitrenes CH(3)N and NH have triplet ground states. The competition between spin-allowed decomposition to the excited state singlet nitrenes and the spin-forbidden N(2) loss is explored using accurate electronic structure methods (CASSCF/cc-pVTZ and MR-AQCC/cc-pVTZ) as well as statistical rate theories. Nonadiabatic rate theories are used for the dissociation leading to the triplet nitrenes. For HN(3), (3)NH formation is predicted to dominate at low energy, and the calculated rate constant agrees very well with energy-resolved experimental measurements. Under thermal conditions, however, the singlet and triplet pathways are predicted to occur competitively, with the spin-allowed product increasingly favored at higher temperatures. For CH(3)N(3) thermolysis, spin-allowed dissociation to form (1)CH(3)N should largely dominate at all temperatures, with spin-forbidden formation of (3)CH(3)N almost negligible. Singlet methyl nitrene is very unstable and should rearrange to CH(2)NH immediately upon formation, and the latter species may lose H(2) competitively with vibrational cooling, depending on temperature and pressure.     

Non-Isothermal Kinetics of the Decomposition Reaction of Cluster [Ag3WS3Br]（PPh3）3 and [Cu3WS3Br]（PPh3）3

The thermal behaviors of clusters [Ag3WS3Br](PPh3)3 and [Cu3WS3Br](PPh3)3 (PPh3=triphenyl phosphine) in a nitrogen atmosphere were studied under the non-isothermal conditions by simultaneous TG-DTG-DSC and EDS techniques. The results showed that the evolution of PPh3 generally proceeded before the release of the other moiety in one or two step-mode. The mechanisms, the kinetic and the thermodynamic parameters for decomposition of PPh3 of both clusters were determined and calculated by jointly using several methods, which showed that its evolution was controlled by Avrami-Erofeev equation. The results also showed that there was no new stable phase composed of W-Ag(Cu)-S-Br after release of organic moiety PPh3 and that CVD method was not applicable to their further processing.     

Influence of the Li+ on the structure of the [Cu3phis3]3+ cation

When [Cu(3)(phis)(3)](ClO(4))(3), obtained from Cu(ClO(4))(2).6H(2)O with the Na(+) or K(+) salt of the phis anion (Hphis = N-(2-pyridylmethyl)-l-histidine), is reacted with LiClO(4), the tricopper cationic structure rearranged to accommodate a Li(+) ion to form [(ClO(4))Li[Cu(3)(phis)(3)]](ClO(4))(3) which can also be prepared directly by reacting Cu(ClO(4))(2).6H(2)O with the Li(+) salt of the phis anion.     

Nonadiabatic coupling in the 3 3Pi and 4 3Pi states of NaK

The excited 3 (3)Pi and 4 (3)Pi electronic states of the NaK molecule exhibit an avoided crossing, leading to the anomalous behavior of many features of the rovibrational energy levels belonging to each state. A joint experimental and theoretical investigation of these states has been carried out. Experimental measurements of the vibrational, rotational, and hyperfine structure of numerous levels of the 3 (3)Pi state were recently obtained using the Doppler-free, perturbation-facilitated optical-optical double resonance technique. Additional measurements for the 4 (3)Pi state as well as bound-free emission spectra from selected 3 (3)Pi, 4 (3)Pi, and mixed 3 (3)Pi to approximately 4 (3)Pi rovibrational levels are reported here. A model is also presented for calculating the mixed rovibrational level energies of the coupled 3 (3)Pi-4 (3)Pi system, starting from a 2x2 diabatic electronic Hamiltonian. The 3 (3)Pi and 4 (3)Pi potential curves and the coupling between them are simultaneously adjusted to fit the observed rovibrational levels of both states. The energy levels of the potential curves determined by the fit are in excellent agreement with experiment. The nonadiabatic coupling is sufficiently strong to cause an overall shift of 2-3 cm(-1) for many rovibrational levels as well as somewhat larger shifts for certain pairs of 3 (3)Pi to approximately 4 (3)Pi levels that would otherwise be very close together.     

Freezing the polarization of CH3NH3PbI3 and CH3NH3PbI3-xClx perovskite films

Thin films of methylammonium lead halides, CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x, were deposited onto symmetrical microstructured electrode arrays of gold or platinum on Si/SiO₂ wafers. Polarization studies were carried out on perovskite films under vacuum in the dark. For poling, a constant voltage was applied to the samples while the temperature was cycled between 295 K and 4 K. The measured current densities depending on the temperature showed distinct characteristics relating strongly to the crystal phase and the dielectric properties of the perovskite films. Voltage sweeps were carried out at different scan rates at specific temperature intervals after poling. The polarization of the films due to the migration of iodide vacancies in direction of the blocking perovskite/metal interface was frozen almost up to room temperature. Charge carriers were only able to cross the blocking barrier and contribute to the current where the ions have accumulated during poling. All J-V curves showed hysteresis: inverted and regular hysteresis at room temperature and below, respectively. Inverted hysteresis originates from the slow accumulation of ions at the blocking barrier, while regular hysteresis arises from a distortion in the adjacent crystals which will be discussed.     

Syntheses and Crystal Structures of the Novel Ternary Thioborates Na3BS3, K3BS3, and Rb3BS3

The orthothioborates Na₃BS₃, K₃BS₃ and Rb₃BS₃ were prepared from the metal sulfides, amorphous boron and sulfur in solid state reactions at temperatures between 923 and 973 K. In a systematic study on the structural cation influence on this type of ternary compounds, the crystal structures were determined by single crystal X‐ray diffraction experiments. Na₃BS₃ crystallizes in the monoclinic space group C2/c (No. 15) with a = 11.853(14) Å, b = 6.664(10) Å, c = 8.406(10) Å, β = 118.18(2)° and Z = 4. K₃BS₃ and Rb₃BS₃ are monoclinic, space group P2₁/c (No. 14) with a = 10.061(3) Å, b = 6.210(2) Å, c = 12.538(3) Å, β = 112.97(2) and a = 10.215(3) Å, b = 6.407(1) Å, c = 13.069(6) Å, β = 103.64(5)°, Z = 4. The potassium and rubidium compounds are not isotypic. All three compounds contain isolated [BS₃]^3– anions with boron in a trigonal‐planar coordination. The sodium cations in Na₃BS₃ are located between layers of orthothioborate anions, in the case of K₃BS₃ and Rb₃BS₃ stacks of [BS₃]^3– entities are connected via the corresponding cations. X‐ray powder patterns were measured and compared to calculated ones obtained from single crystal X‐ray structure determinations.     

Spectroscopic evidence for the existence of the CF3OSO3 radical

The first spectroscopic evidence for the existence of the CF(3)OSO(3) radical has been obtained from matrix isolation and FT-IR and UV spectroscopic studies. The vibrational frequencies measured are in reasonable agreement with predictions from density functional calculations. Upon visible and UV photolysis of the CF(3)OSO(3) radical, SO(3) is produced and provides experimental support for a new light-driven route for the oxidation of SO(2) to SO(3) assisted by CF(3)O radicals.     

Kinetics of the gas-phase reactions of NO3 radicals and O3 with 3-methylfuran and the OH radical yield from the O3 reaction

Using relative rate methods, rate constants have been measured for the gas-phase reactions of 3-methylfuran with NO₃ radicals and O₃ at 296 ± 2 K and atmospheric pressure of air. The rate constants determined were (1.31 ± 0.461) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the NO₃ radical reaction and (2.05 ± 0.52) × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ for the O₃ reaction, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference reactions. Based on the cyclohexanone plus cyclohexanol yield in the presence of sufficient cyclohexane to scavenge > 95% of OH radicals formed, it is estimated that the O₃ reaction leads to the formation of OH radicals with a yield of 0.59, uncertain to a factor of ca. 1.5. In the troposphere, 3-methylfuran will react dominantly with the OH radical during daylight hours, and with the NO₃ radical during nighttime hours for nighttime NO₃ radical concentrations > 10⁷ molecule cm ⁻³. © 1996 John Wiley & Sons, Inc.     

Analysis of the intermolecular interactions between CH3OCH3, CF3OCH3, CF3OCF3, and CH2F2, CHF3

The intermolecular interaction energy curves of CH(3)OCH(3)-CH(2)F(2), CF(3)OCH(3)-CH(2)F(2), CF(3)OCF(3)-CH(2)F(2), CH(3)OCH(3)-CHF(3), CF(3)OCH(3)-CHF(3), and CF(3)OCF(3)-CHF(3) complexes were calculated by the MP2 level ab initio molecular orbital method using the 6-311G** basis set augmented with diffuse polarization functions. We investigate the fluorine substitution effects of both methane and dimethyl ether on intermolecular interactions. In addition, orientation dependence of intermolecular interaction energies is also studied with utilizing eight types of orientations. Our analyses demonstrate that partial fluorinations of methane make electrostatic interaction dominant, and consequently enhance attractive interaction at several specific orientations. On the contrary, fluorine substitutions of dimethyl ether substantially decrease the electrostatic interaction between ether and CH(2)F(2) or CHF(3); thus, there is no such characteristic interaction between the C-H of fluorinated methane and ether oxygen of CF(3)OCF(3) as conventional hydrogen bonding, due to reduced polarity of fluorinated ether. The combination of different pairs of the electrostatic interaction is therefore responsible for the intermolecular interaction differences among the complexes investigated herein and also their orientations.     

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH3NH3PbI3

Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH₃NH₃PbI₃ being an archetypal compound. The question why CH₃NH₃PbI₃ has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non‐centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long‐range level. Although the molecular cation CH₃NH₃⁺ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions.     

High-performance liquid chromatographic method for the separation of the optical isomers of γ,γ′-di-tert.-butyl- -γ-carboxyglutamic acid and -γ-carboxyglutamic acid

The chemical synthesis of γ,γ′-tert.-butyl-γ-carboxyglutamic acid is accompanied by extensive racemization, and very careful resolution is needed to obtain and -γ,γ′-di-tert.-butyl-γ-carboxyglutamic acids in high chiral purity. A novel method was devised for the separation of enantiomers of γ,γ′-di-tert.-butyl-γ-carboxyglutamic acid and γ-carboxyglutamic acid, applying precolumn derivatization with 1-fluoro-2,4-dinitrophenyl-5- -alanine amide and 2,3,4,6-tetra-O-acetyl-β- -glucopyranosyl isothiocyanate as chiral reagents, with subsequent reversed-phase high-performance liquid chromatographic separation of diastereomeric compounds. The effects of organic modifiers, of the mobile-phase composition and of the pH on the separation of the diastereomers were investigated.     

Energies and radial couplings for the Σ and Σ states of the NaHe quasimolecule

We present the energies and radial couplings for the five ¹Σ and four ³Σ states of lowest energy of the NaHe⁺ quasimolecule, with a precision which is sufficient to treat Na/He⁺ collisions. The characteristics of energies and couplings are studied in detail with the aid of qualitative orbital and state-correlation diagrams.     

Control of Charge Transport in the Perovskite CH3NH3PbI3 Thin Film

Carrier density and transport properties in the CH₃NH₃PbI₃ thin film have been investigated. It is found that the carrier density, the depletion field, and the charge collection and transport properties in the CH₃NH₃PbI₃ absorber film can be controlled effectively by different concentrations of reactants. That is, the carrier properties and the self‐doping characteristics in CH₃NH₃PbI₃ films are strongly influenced by the reaction thermodynamic and kinetic processes. Furthermore, by employing mixed solvents with ethanol and isopropanol to deposit the CH₃NH₃PbI₃ film, the charge collection and transport efficiencies are improved significantly, thereby yielding an overall enhanced cell performance.     

Hydration of C3a in the presence of CaCO3

The hydration of C₃A with and without CaCO₃ was studied. The techniques used were X-ray diffraction, thermogravimetry, differential thermogravimetry and calorimetry.In the presence of CaCO₃, the hydration of C₃A is accelerated. The hexagonal hydrates are formed first. They react with CaCO₃ to form calcium carboaluminate hydrate. This reaction blocks formation of the cubic hydrate. The latter appears when CaCO₃ is completely consumed.     

Matrix isolation infrared spectroscopic study of the interaction of CH3ReO3 with NH3

The matrix isolation technique has been combined with infrared spectroscopy to identify and characterize the product of the codeposition of CH3ReO3 with NH3 into inert matrices at 14 K. This codeposition led to the formation of the isolated 1:1 complex between these two reagents and its isolation in argon and nitrogen matrices. The complex is characterized by perturbations to all of the vibrational modes of the NH3 subunit in the complex, including a large, 185 cm(-1) blue shift of v2, the symmetric deformation mode. In addition, shifts of the -ReO3 antisymmetric stretch and -ReO3 symmetric bending of the CH3ReO3 subunit in the complex were observed. This complex, while predicted theoretically, has not been reported previously.     

Influence of Orientational Disorder on the Optical Absorption Properties of the Hybrid Metal-Halide Perovskite CH3NH3PbI3

An experimental and theoretical investigation is reported to analyze the relation between the structural and absorption properties of CH₃NH₃PbI₃ in the tetragonal phase. More than 3000 geometry optimizations were performed to reveal the structural disorder and identify structures with the lowest energies. The electronic structure calculations provide an averaged band gap of 1.674 eV, which is in excellent agreement with the experimental value of about 1.6 eV. The simulations of the absorption spectrum for three representative structures with lowest energy reproduced the absorption shoulders observed in the experimental spectra. These shoulders are assigned to excitations having similar orbital characters and involving transitions between hybridized 6s(Pb)/5p(I) orbitals and 6p(Pb) orbitals. The geometries of the three structures were analyzed and the effects of the inorganic frame and the CH₃NH₃⁺ cations on the absorption properties were estimated. It was found that both changes in the inorganic frame and the CH₃NH₃⁺ cations orientations impact the absorption spectra, by modifying the transitions energies and intensities. This highlights the role of CH₃NH₃⁺ cation in influencing the absorption properties of CH₃NH₃PbI₃ and demonstrates that CH₃NH₃⁺ cation is one of the key elements explaining the broad and nearly constant absorption spectrum in the visible range.     

3-叠氮甲基-3-硝酸酯甲基环氧丁烷的聚合反应研究

改进了单体3-叠氮甲基-3-硝酸酯甲基环氧丁烷的合成路线,以三氟化硼·乙醚为催化剂,1,4-丁二醇为引发剂,研究了该含能单体的开环聚合反应,得到了分子量可预计、分散度较小的聚合物.采用FTIR、¹HNMR和GPC对聚合物结构进行了表征.     

On the Side-Chain Bromination of 3-Methylselenophene and 3-Methylthiophene

3-Bromomethylselenophene can be prepared from 3-methyl-selenophene, N-bromosuccinimide and azo-bis-isobutyronitrile in carbon tetrachloride in 25% yield with the reversed addition method described in this paper. The method also gives consistently high yields of 3-bromomethylthiophene (70–75%) when applied on 3-methylthiophene.