Thermodynamic modeling of SiBCN film deposition from the gas phase in the Si—B—N—C—H system

Thermodynamic modeling of the chemical vapor deposition (CVD) of films of complex composition in the Si—B—N—C—H system under reduced pressure (0.01 or 10 Torr) in a wide temperature range of 500–1500 K using various organoelement compounds was carried out. An example with mixtures of tetramethylsilane SiMe₄ and hexamethyldisilane (SiMe₃)₂ with trimethylamine borane Me₃N · BH₃ or triethylamine borane Et₃N · BH₃ illustrates a possibility to produce films of various compositions: from boron and silicon nitrides to their mixtures with carbides and/or carbon. According to the CVD diagrams, the prevailing equilibrium condensed phases are various phase complexes containing SiC, Si₃N₄, BN, and C.

     

Mass spectrometric studies of non-covalent compounds: why supramolecular chemistry in the gas phase?

Supramolecular chemistry has progressed quite a long way in recent decades. The examination of non-covalent bonds became the focus of research once the paradigm that the observed properties of a molecule are due to the molecule itself was revised, and researchers became aware of the often quite significant influence of the environment. Mass spectrometry and gas-phase chemistry are ideally suited to study the intrinsic properties of a molecule or a complex without interfering effects from the environment, such as solvation and the effects of counterions present in solution. A comparison of data from the gas phase, i.e. the intrinsic properties, with results from condensed phase, i.e. the properties influenced by the surroundings of the molecule, can consequently contribute significantly to the understanding of non-covalent bonds. This review provides insight into the often-underestimated power of mass spectrometry for the investigation of supramolecules. Through example studies, several aspects are discussed, including determination of structure in solution and the gas phase, ion mobility studies to reveal the formation of zwitterionic structures, stereochemical issues, analysis of reactivity of supramolecular compounds in the condensed and in the gas phase, and the determination of thermochemical data.     

Vapor phase composition and radical polymerization—how the gas phase influences the kinetics of heterophase polymerization

The outcome of radical styrene heterophase polymerization depends strongly on the composition of the gas phase. Data of a comprehensive experimental study show that the effect of the gas phase is quite a complex one and strongly influenced by the nature of the gas, the homogeneity or heterogeneity of the polymerization system, and the kind of initiator. Evidence is presented that the influence of air goes beyond the simple action of oxygen which can cause deceleration or acceleration of the reaction. The experimental results show that the optimum polymerization conditions are obtained in the absence of any foreign gas.     

Thermodynamic simulation and experimental investigation of reactive chemical vapor deposition in the Ta–C–Si–O–F system

Reactive deposition processes of tantalum carbide are studied experimentally and theoretically in the Ta–C–Si–O–F system. It is shown that Sio₂ substantially affects the carbide formation process. This is expressed in a decreased efficiency of tantalum transfer from the source zone to the crystallization zone, the possibility of bilateral transport of tantalum to carbon and carbon to tantalum, the complicated composition of condensed phases in the equilibrium with the gas phase. Aspects of preparing single crystal tantalum oxyfluoride are considered.     

A computational study on the gas phase reaction of Os^＋ with N2O

The reaction of Os~+(~6D,~4F) with N_2O has been investigated at B3LYP/TZVP and CCSD(T)/6-311+G~* levels of theory.The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed.It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism,leading to the formation of OsO~+ and OsN~+,whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism.The calculated energ...     

New prenylated C₆-C₃ compounds from the twigs of Illicium anisatum

Two new prenylated C?-C? compounds, cycloillicinone (1) and 4-allyl-2-methoxy-6-(2-methylbut-3-en-2-yl)phenol (2), were isolated from the twigs of Illicium anisatum, and their structures were determined by 2D-NMR methods. Cycloillicinone (1) is a unique prenylated C?-C? that is appended with an additional geranyl unit. Compound 2 was found to show moderate neurite-outgrowth promoting activity in primary cultured rat cortical neurons at a concentration of 10 μM.     

A comparative QCISD(T), DFT and MCSCF study of the unimolecular, decomposition of the N-chloro-α-glycine anion in gas phase

Stationary points were localized and characterized on potential energy surfaces for the unimolecular decomposition of the anionic form of N-chloro--glycine in its singlet and triplet electronic states by means of QCISD(T), DFT and MCSCF methods. The present study predicts that the unimolecular decomposition mechanism takes place in the singlet electronic state through a concerted and slightly asynchronous process and the transition structure has an antiperiplanar conformation. A comparison of the structures for stationary points calculated with different methods yields similar geometries and the components of transition vector are weakly dependent on the computing method.     

Characteristics of retention and enthalpies of sorption from the gas phase of esters of trimethylolpropane and С2–С5 acids on DB-1 stationary phase

Characteristics of retention and their temperature dependences, along with the thermodynamic characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220–280°C for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of structures containing from 2 to 6 carbon atoms.

     

Thermodynamic aspects of the Ru(III)—EDTA—ascorbate—molecular oxygen system for the oxidation of saturated and unsaturated organic compounds

The activation and thermodynamic parameters corresponding to rate and equilibrium constants, respectively, for the homogeneous oxidation of the saturated substrates, cyclohexane to cyclohexanol, cyclohexanol to cis-1,3-cyclohexane diol and olefin, cyclohexene to epoxide by Ru(III)—EDTA—ascorbateO₂ system were determined by measuring the various rates and equilibrium constants at four different temperatures in the range 288–313 K and μ = 0.1 M KNO₃ in a 50% (V/V) mixture of 1,4-dioxane and water in acidic medium. The kinetics of the oxidation of these substrates at each particular temperature was studied as a function of the concentration, the substrates, hydrogen ion, catalyst, ascorbic acid and molecular oxygen. The orders of the reaction in cyclohexanol and cyclohexene concentrations are one, and those in cyclohexane and hydrogen ion concentration are fractional and inverse first-order, respectively. For all substrates the reaction is first order with respect to the concentrations of molecular oxygen, ascorbic acid and catalyst. The source of the oxygen atom transferred to the substrates was confirmed by ¹⁸O₂ isotope studies in which the ¹⁸O was incorporated in the oxidized products. The kinetics and solvent isotope effect were studied for the oxidation of C₆H₁₂, C₆D₁₂, C₆H₁₁OH and C₆D₁₁OD. The order of the reactivity observed in the oxidation of the substrates studied is cyclohexene > cyclohexanol > cyclohexane. A comparison of the rates of oxidation of the substrates and the corresponding activation parameters with the catalytic systems Ru(III)—EDTAO₂ and Ru(III)—EDTA—ascorbateH₂O₂ indicated that activation parameters become more favourable in the presence of ascorbic acid, where the system acts as a mono-oxygenase and the activation energies are drastically reduced. Highly negative entropies are associated with all oxygen atom transfer reactions, indicating that the oxidation process is associative in nature.     

F-NMR-spectroscopy for the identification of photo products generated from aromatic iodo compounds—IV

The investigation demonstrates the analytical power of F-NMR spectroscopy for the identification of isomeric substituted fluorobiphenyls. The biphenyls are formed by u.v. irradiation of iodobenzenes in aromatic solvents. A special procedure for the identification is outlined and tendencies of the results—chemical shifts and relative rates for the production of isomers—are discussed in consideration of electronic and steric substituent effects.     

Thermodynamics of the sorption of organic compounds on polyethylene glycol 400–permethylated β-cyclodextrin stationary phase and its enantioselectivity in gas chromatography

The thermodynamic characteristics of sorption of 24 organic compounds of various classes from the gas phase on the binary stationary phase based on polyethylene glycol 400 and permethylated β-cyclodextrin were determined. The influence of geometrical structure and optical activity of organic compounds on the possibility of forming sorbate–macrocycle complexes was examined. It was found that the studied stationary phase shows the enantioselectivity towards low-polar terpenes under the conditions of gas chromatography.     

Optical emission spectroscopy in reactive hollow cathode arc discharge plasmas – Local distribution of active species during the deposition of hard carbon films

A low pressure arc plasma discharge from a hollow LaB(6)-cathode with up to 100 A discharge current is used to create plasmas of high density. Typical values for the electron density and temperature in PETRA ( Plasma Engineering and Technology Research Assembly) are n(e)=10(12)-10(13) cm(-3) and T(e)=5-20 eV. The ionization ratio is typically 1-10%. Optical emission spectroscopy has been applied to investigate the processes within the plasma which lead to the deposition of thin carbon films. In these experiments hydrogenated carbon films (a-C:H) have been deposited on Si-substrates by introducing hydrocarbon gases (CH(4), C(2)H(2)) into He- and Ar-plasmas. Space resolved optical emission spectroscopy using an in-situ translation mechanism of the optical fibre has been performed to measure the local concentrations of CH-radicals, carbon ions and of the excitation of He-neutrals. In addition the hydrogen liberated by the dissociation of the hydrocarbon molecules has been measured. The dissociation of the hydrocarbon molecules takes place as a localized process in the vicinity of the reactive gas inlet.     

The formation of MoS<Subscript>2</Subscript> secondary phase at the Cu—Zn—Sn—S/Mo interface during the sulfurization process of Cu—Zn—Sn precursor films

We report on the influence of the sulfurization conditions on the MoS₂ secondary phase formation in Cu—Zn—Sn—S thin films synthesized by thermal evaporation method of metals and intermetallics that can be used for the formation of absorbing layers of solar cells. The dependence between photoconductivity and the intensity of the base line of MoS₂ was found in Raman spectra, which is described by a curve with characteristic maximum. It was found that the secondary phase formation on the Cu—Zn—Sn—S/Mo boundary and photoconductivity of sulfurized films are strongly dependent on the applied temperature conditions. Specifically, films without MoS₂ phase have a low photoconductivity, whereas a high photoconductivity was observed for the films with significant content of secondary phase.     

Thermodynamic quantities for the ionization of nitric acid in aqueous solution from 250 to 319°C

The aqueous reaction, HNO₃(aq)=H⁺+NO ₃ ^– was studied as a function of ionic strength I at 250, 275, 300 and 319°C using a flow calorimeter and the equilibrium constant K and enthalpy change (H) at I=0 were determined. Using these experimental values, equations describing logK, H, the entropy change S and the heat capacity change C _p of reaction at I=0 and temperatures from 250 to 319°C were derived. The increasing importance of ion association as temperature rises was discussed. The use of an equation containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the logK values reported here and to those determined by others. The resulting plot of logK for the isocoulombic reaction vs. 1/T was fairly linear which supports the postulate that the principle is a useful technique for the extrapolation of logK values from low to high temperatures.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Generation of transient neutrals in the gas phase from anionic precursors. Does energised CNCCO rearrange to NCCCO?

The stability and reactivity of the neutral species CNCCO generated by one electron oxidation of the anion [CNCCO](-) have been investigated by a combination of theoretical calculations (carried out at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory) and tandem mass spectrometric experiments. Some of the neutrals formed in this way are stable for the microsecond duration of the experiment, but others are energised. The neutrals which are energised may either (i) dissociate [CNCCO --> CNC + CO (+92 kJ mol(-1))], and/or (ii), undergo the isonitrile to nitrile rearrangement to yield NCCCO energised neutrals (barrier 133 kJ mol(-1), reaction exothermic by 105 kJ mol(-1)). Some of these rearranged neutrals NCCCO have excess energies as high as 238 kJ mol(-1) and will dissociate [NCCCO --> NCC + CO (+203 kJ mol(-1))].