The behavior of molecules in microwave-induced plasmas studied by optical emission spectroscopy. 1. Plasmas at atmospheric pressure

The behavior of molecules in different atmospheric microwave-induced plasmas (MIPs) has been studied by means of optical emission spectroscopy. This is in order to obtain more insight into molecular processes in plasmas and to investigate the feasibility of emission spectroscopy for the analysis of molecular compounds in gases, e.g. flue gases. Various molecular species (i.e. N₂, CO₂, H₂O, SF₆ and SO₂) have been introduced into discharges in argon or in molecular gases such as carbon dioxide or nitrogen. The plasmas were created and sustained by a guide-surfatron or a torch in the power range of 150 W to 2 kW. Only nitrogen sometimes yielded observable emission from the non-dissociated molecule (first and second positive system). Using other molecular gases, only dissociation and association products were observed (i.e. atomic species and diatomic molecules such as CN, C₂, CO, OH, NH and N₂⁺). The intensities of these products have been studied as a function of the concentration of introduced molecules, the position in the plasma and the composition of the plasma environment. Since in most cases the same diatomic association products are seen, observed associated molecules can only to some extend be related to the molecules originally present in the plasma gas. Therefore, it will be difficult to use atmospheric microwave discharges for the analysis of gas mixtures under the experimental conditions studied.     

High resolution infrared spectroscopy of the sun and the earth's atmosphere from space

The atmospheric trace molecule spectroscopy experiment (ATMOS) was designed to obtain high-resolution absorption spectra of the atmosphere from earth orbit, from which the vertical distributions of a large number of minor and trace molecular constituents could be retrieved. The ATMOS instrument is an FFT spectrometer covering the 600 to 5000 cm^–1 frequency range and uses a double-passed, tilt-compensated optical configuration, with the two retroreflectors moving reciprocally. The scan time of 2 s gives spectra with an unapodized resolution of 0.01 cm^–1, spaced 4 km apart, vertically.The first flight of ATMOS was made in April, 1985, as part of the Shuttle Spacelab-3 science payload. A total of 19 sunrise and sunset occultations were observed, which resulted in the acquisition of more than 1000 atmospheric spectra with an equal number of solar only scans. The spectra show absorptions of some 40 different atmospheric constituents, some of which are discernable at altitudes well into the thermosphère (i.e., up to about 150 km). The high signal/noise ratio and repeatability of the spectra have enabled a wealth of new atmospheric data to be retrieved, including the first positive identifications of such key reservoir species as COF₂, HNO₄, and N₂O₅, simultaneous vertical distributions of the minor gases from 5 to 140 km, the entire odd-nitrogen family in the stratosphere, and most of the halogen source gases with their corresponding reservoir and sink species. Measurements of the frequencies of large numbers of spectral lines has yielded Doppler shifts from which zonal winds, having a precision of the order of 2 m/s, have been retrieved throughout the stratosphere and mésosphère.     

Pyrolysis and TG Analysis of Shivee Ovoo Coal from Mongolia

The coal sample of the Shivee Ovoo deposits has been non-isothermally pyrolysed in a thermogravimetric analyser to determine the influence of temperature, heating rate and purge gas employed on the thermal degradation of the sample. The heating rates investigated in the TG were 10–50 K min^–1 to final temperature of 1000°C. N₂or CO₂ were employed as well as type of purge gas on the process of thermal degradation of the coal sample. The coal was also investigated in a fixed bed reactor to determine the influence of temperature and heating rate of the pyrolysis on the yield of products and composition of the gases evolved. The main gases produced were H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆ and C₃H₈ and also minor concentrations of other gases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diagnostics and decomposition mechanism in radio-frequency discharges of fluorocarbons utilized for plasma etching or polymerization

Optical emission (180–800 nm) and mass spectroscopy have been used to study the CF₄, CF₄+O₂, C₂F₆, C₂F₆+H₂, CF₃Cl, and C₂F₄ decomposition in radio-frequency discharges. The analysis of the stable and unstable discharge products has allowed the suggestion of decomposition channels for the various gases and to classify the fluorinated gases according to their predominant etching or polymerizing characteristics on the basis of the active species present in the plasma. A new broad emission continuum centered at =290 nm (FWHM=66 nm) has also been identified and it has been tentatively assigned to CF⁺ ₂.     

Processing of Oil Refinery Gases: Oxidative Dehydrogenation of the Ethane–Ethylene Fraction

Oxidative transformations of the ethane–ethylene fraction of oil refinery gases, containing 20 vol % C₂H₄, on VMoTeNb oxide catalyst in the temperature interval 330–450°C were studied. Comparison with oxidative transformations of the individual components (oxidative dehydrogenation of C₂H₆ and oxidation of C₂H₄) shows that ethylene does not noticeably influence the ethane conversion, whereas ethane strongly suppresses the ethylene conversion. The maximal yield of ethylene from the ethane–ethylene fraction is close to that reached in oxidative dehydrogenation of ethane under similar conditions and amounts to 70–72%.     

Sorption and partial molar volume of gases in polybutadiene

Sorption of He, H₂, N₂, O₂, Ar, CH₄, C₂H₆, and C₂H₆ in polybutadiene and the dilation of the polymer due to sorption of the gases are investigated over the pressure range 0-50 atm at 25°C. For CO₂ the measurements are made at temperatures ranging from 15 to 80°C. Partial molar volumes of the gases in the polymer are determined. The temperature dependence of partial molar volume is discussed on the basis of the data for CO₂. The Flory-Huggins interaction parameters of CO₂, C₂H₄, and C₂H₆ are also estimated.     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

Refractive index and derived molecular properties of some gases determined by dispersive fourier transform spectroscopy (DFTS) in the visible wave number range

Dispersive Fourier transform spectroscopy (DFTS) is used to determine the dispersion of the real refractive indexn() of the gases CH₄, C₂H₄, C₂H₆, C₃H₈ and cyclo-C₃H₆ in the visible wave number range. Some molecular properties, e.g. oscillator strength sums, are derived from these measurements and compared with available data of literature.     

Solubility of nonpolar gases in tetrahydropyran at 0 to 30°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, and SF₆) in tetrahydropyran at the temperature range 0 to 30°C and 101.33 kPa partial pressure of gas are reported. Thermodynamic functions for the solution process (Gibbs energy, enthalpy, and entropies) at 25°C are evaluated from the experimental values of the solubility of gases as mole fraction and their variation with the temperature. Lennard-Jones 6–12 pair potential parameters for tetrahydropyran are estimated by using the scale particle theory (SPT); and experimental solubilities are compared with the calculated values using this model. Experimental solubilities of gases in tetrahydropyran and intermolecular potential parameters are compared with those obtained for the same gases in other cycloethers.     

Application of a Microwave Helium Plasma Torch Operating at Atmospheric Pressure to Destroy Trichloroethylene

We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental results obtained, the proposed system allows input concentrations of C₂HCl₃ in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using a microwave plasma power below 1000 W. High helium flow-rates and C₂HCl₃ concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds resulting from the destruction of C₂HCl₃, and that of CCl₄ and C₂Cl₄ as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO₂, NO and N₂O in addition to Cl₂ traces.     

NMR investigation of alkaloids I.13C NMR spectra and stereochemistry of pentacyclic oxindole alkaloids of the heteroyohimbine group of the epiallo and allo series

The¹³C NMR spectra of pentacyclic oxindole alkaloids of the heteroyohimbine group of the allo and epiallo series have been studied and an assignment has been made of the CSs of the carbon atoms. Characteristic differences have been noted in the¹³C CSs of the C₂, C₃, C₇, C₁₄, C₁₅, and C₁₉ carbon atoms that may be useful for solving stereochemical problems in new bases of this series from their¹³C NMR spectra.Communicated at the All-Union Conference on Recent Advances in High-resolution NMR spectroscopy, Tashkent, September, 1979 [1].Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 217–224, March–April, 1980.     

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]_n (PCP-1) and [Zn₂(L1)(L3)₂]_n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions.     

Gas permeation through hydrogels : I. Gel cellophane membranes

Permeabilities and diffusion coefficients of various gases, Ar, N₂, O₂, CO₂, CH₄, C₂H₄, C₃H₈ and C₄H₁₀, were measured for Water-swollen gel cellophane membranes. No dependence of permeabilities on gas pressure below 1 atm was found. It was observed that the permeability coefficients were not related linearly to the coefficients in bulk water. For the two states of water in the membrane, an analytical method is presented to estimate the diffusion coefficients and the solubilities in free water and non-freezing water. It was found that the diffusion coefficients in non-freezing water were lower than those in free water, and the solubilities in non-freezing water were higher than in free water for all gases studied except CO₂ and C₂H₄, which gave reverse results.     

Gravimetric study of high-pressure sorption of gases in polymers

A gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N₂ and CO₂ in low-density polyethylene (LDPE); CO₂ in polycarbonate (PC); and N₂, CH₄, C₂H₆, and CO₂ in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time-dependent hysteresis in the sorption of CO₂, C₂H₆, and CH₄ in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high-pressure CO₂ on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual-mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.     

Determination of impurities in high-purity hydrogen sulfide by gas chromatography-mass spectrometry using gas adsorption capillary columns

Gas chromatography-mass spectrometry has been used to study the impurity composition of high-purity hydrogen sulfide. Impurities of atmospheric gases, COS,CS₂, SO₂, benzene, toluene, thiophene, and its homologues have been detected. Detection limits of impurities are 10⁻⁷-10⁻⁵ vol %.     

Vibrational spectra and structure of trinitromethane

The vibrational spectrum of trinitromethane was interpreted in terms of the additive interatomic interaction model on the basis of experimental infrared and Raman spectra of HC(NO₂)₃, DC(NO₂)₃, HC(¹⁵NO₂)₃ and normal coordinate analysis. The frequency assignment results were used in discussing its structure. It was shown that the symmetry of trinitromethane is below C₃ in the liquid state.     

Solubility of nonpolar gases in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas are reported. Gibbs energy for the solution process at 25°C is evaluated from the experimental values of the solubility of gases expressed as mole fraction. Lennard-Jones 6–12 pair potential parameters for 2,2,2-trifluoroethanol are estimated by using the scaled particle theory (SPT); and experimental solubilities are compared with those calculated from the values of these parameters through the SPT model.     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Solubility of gases in butanols: IV. Solubilities of nonpolar gases in 2-methyl-2-propanol at 303.15 K and 101.33 kPa partial pressure of gas

Solubilities of 15 nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, O₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2-methyl-2-propanol (tert-butanol) have been measured at the temperature 303.15 K and 101.33 kPa partial pressure of gas. Standard changes of the Gibbs energy of solution have been also determined from experimental data. The Lennard–Jones 6,12 pair potential parameters have been estimated for that solvent using the Scaled Particle Theory (SPT) and these parameters have been compared with those corresponding to the other isomers of butanol. It can be concluded that the derived energy parameters provide a measurement of the association of the alkanol. A version of the UNIFAC model has been applied and the corresponding interaction parameters for alkanes and alkanols have been determined.     

Abtrennung von Submikrogramm-Mengen Arsen aus Ammomumfluoridlösungen

Arsenic has been separated from NH₄F solutions by coprecipitation with MnO(OH)₂, which is formed within the solution by addition of stoichiometric amounts of MnSO₄ and KMnO₄. The precipitate is dissolved in HC1 and As determined by known methods.