Gas-phase Reaction Products Research Articles

Mass spectrometric study of gas-phase chemistry in a hot-wire chemical vapor deposition reactor with tetramethylsilane

To understand the gas-phase chemistry in the processes of hot-wire chemical vapor deposition (HWCVD) with tetramethylsilane (TMS), the gas-phase products from the decomposition of TMS on a hot tungsten filament and the secondary gas-phase reactions in a HWCVD reactor have been studied using vacuum ultraviolet laser single photon ionization time-of-flight mass spectrometry. It is found that TMS decomposes on the filament to methyl and trimethylsilyl radicals. Subsequent reactions between these two primary radicals and with the parent molecule have resulted in the formation of alkyl-substituted silanes ( m/ z = 102, 116, 146) and silyl-substituted alkanes ( m/ z = 160, 174, 188, 232, 246). Small alkenes (C n H 2 n , n ≤ 4) are produced at high filament temperatures ( T ≥ 1800 °C). The dominant pathways in the secondary gas-phase reactions are found to be the biradical combination reactions involving the alkylsilyl-substituted methyl radicals formed from the H abstraction reaction of either alkyl-substituted silane or silyl-substituted alkanes by methyl radicals. Silicon carbon (Si C) bond is found to be the major bond connection in the gas-phase reaction products in mass regions higher than the parent mass. 1,1,3,3-Tetramethyl-1,3-disilacyclobutane molecule ( m/ z = 144) is believed to be formed in the HWCVD reactor, implying the existence of the unsaturated silene intermediates.

Heterogeneous Chemistry of the NO3 Free Radical and N2O5 on Decane Flame Soot at Ambient Temperature: Reaction Products and Kinetics

The interaction of NO3 free radical and N2O5 with laboratory flame soot was investigated in a Knudsen flow reactor at T = 298 K equipped with beam-sampling mass spectrometry and in situ REMPI detection of NO2 and NO. Decane (C10H22) has been used as a fuel in a co-flow device for the generation of gray and black soot from a rich and a lean diffusion flame, respectively. The gas-phase reaction products of NO3 reacting with gray soot were NO, N2O5, HONO, and HNO3 with HONO being absent on black soot. The major loss of NO3 is adsorption on gray and black soot at yields of 65 and 59%, respectively, and the main gas-phase reaction product is N2O5 owing to heterogeneous recombination of NO3 with NO2 and NO according to NO3 + {C} --> NO + products. HONO was quantitatively accounted for by the interaction of NO2 with gray soot in agreement with previous work. Product N2O5 was generated through heterogeneous recombination of NO3 with excess NO2, and the small quantity of HNO3 was explained by heterogeneous hydrolysis of N2O5. The reaction products of N2O5 on both types of soot were equimolar amounts of NO and NO2, which suggest the reaction N2O5 + {C} --> N2O3(ads) + products with N2O3(ads) decomposing into NO + NO2. The initial and steady-state uptake coefficients gamma 0 and gamma ss of both NO3 and N2O5 based on the geometric surface area continuously increase with decreasing concentration at a concentration threshold for both types of soot. gamma ss of NO3 extrapolated to [NO3] --> 0 is independent of the type of soot and is 0.33 +/- 0.06 whereas gamma ss for [N2O5] --> 0 is (2.7 +/- 1.0) x 10(-2) and (5.2 +/- 0.2) x 10(-2) for gray and black soot, respectively. Above the concentration threshold of both NO3 and N2O5, gamma ss is independent of concentration with gamma ss(NO3) = 5.0 x 10(-2) and gamma ss(N2O5) = 5.0 x 10(-3). The inverse concentration dependence of gamma below the concentration threshold reveals a complex reaction mechanism for both NO3 and N2O5. The atmospheric significance of these results is briefly discussed.

In situ diagnostics of the decomposition of silacyclobutane on a hot filament by vacuum ultraviolet laser ionization mass spectrometry

The gas-phase reaction products of silacyclobutane (SCB) and 1, 1-dideuterio-silacyclobutane (SCB-d(2)) from a hot-wire chemical vapor deposition (HWCVD) chamber were diagnosed in situ using vacuum ultraviolet (VUV) laser single-photon ionization (SPI) coupled with time-of-flight (TOF) mass spectrometry. The SCB molecule was found to decompose at a filament temperature as low as 900 degrees C. Both Si- (silylene, methylsilylene, and silene) and C-containing (ethene and propene) species were produced from the SCB decomposition on the filament. Ethene and propene were detected by the mass spectrometer. It is demonstrated that the formation of ethene is favored over that of propene. The experimental study of hot-wire decomposition of SCB-d(2) shows that propene is most likely produced by a process that is initiated by a 1,2-H(D) migration to form n-propylsilylene, followed by an equilibration with silacyclopropane, which then decomposes to propene. The detection of ethene in our experiment indicates that a competitive route of fragmentation exists for SCB decomposition on the filament. It has been shown that this competitive route occurs without H/D scrambling. The highly reactive silylene, silene, and methylsilylene species produced from SCB decomposition underwent either insertion reactions into the Si-H bonds of the parent molecule or pi-type addition reaction across the double and triple CC bonds. The dimerization product of silene, 1,3-disilacyclobutane, at m/z = 88 was also observed.

Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers

Abstract. Formation of secondary organic aerosol has been observed in the gas phase ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers (AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The ozonolysis has been studied in a 570 l spherical glass reactor at ambient pressure (730 Torr) and room temperature (296 K). Gas phase reaction products were investigated by in-situ FTIR spectroscopy, and secondary organic aerosol (SOA) formation was monitored by a scanning mobility particle sizer (SMPS). The chemical composition of the formed SOA was analysed by a hybrid mass spectrometer using electrospray ionization (ESI). The main stable gas phase reaction product is the respective alkyl formate ROC(O)H, formed with yields of 60 to 80%, implying that similar yields of the corresponding excited Criegee Intermediates (CI) CH2O2 for the AVE and CH3CHO2 for EPE are generated. Measured SOA yields are between 2 to 4% for all enol ethers. Furthermore, SOA formation is strongly reduced or suppressed by the presence of an excess of formic acid, which acts as an efficient CI scavenger. Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify oligomeric compounds in the mass range 200 to 800 u as its major constituents. Repetitive chain units are identified as CH2O2 (mass 46) for the AVE and C2H4O2 (mass 60) for EPE and thus have the same chemical compositions as the respective major Criegee Intermediates formed during ozonolysis of these ethers. The oligomeric structure and chain unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF experiments, whereby successive and systematic loss of a fragment with mass 46 for the AVE (and mass 60 for EPE) is observed. It is proposed that the oligomer has the following basic structure of an oligoperoxide, -[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE. Oligoperoxide formation is thus suggested to be another, so far unknown reaction of stabilized Criegee Intermediates in the gas phase ozonolysis of oxygen-containing alkenes leading to SOA formation.

Investigating the composition of organic aerosol resulting from cyclohexene ozonolysis: low molecular weight and heterogeneous reaction products

Abstract. The composition of organic aerosol formed from the gas phase ozonolysis of cyclohexene has been investigated in a smog chamber experiment. Comprehensive gas chromatography with time of flight mass spectrometric detection was used to determine that dicarboxylic acids and corresponding cyclic anhydrides dominated the small gas phase reaction products found in aerosol sampled during the first hour after initial aerosol formation. Structural analysis of larger more polar molecules was performed using liquid chromatography with ion trap tandem mass spectrometry. This indicated that the majority of identified organic mass was in dimer form, built up from combinations of the most abundant small acid molecules, with frequent indication of the inclusion of adipic acid. Trimers and tetramers potentially formed via similar acid combinations were also observed in lower abundances. Tandem mass spectral data indicated dimers with either acid anhydride or ester functionalities as the linkage between monomers. High-resolution mass spectrometry identified the molecular formulae of the most abundant dimer species to be C10H16O6, C11H18O6, C10H14O8 and C11H16O8 and could be used in some cases to reduce uncertainty in exact chemical structure determination by tandem MS.

Influence of O 2 and H 2 on NO reduction by NH 3 over Ag/Al 2O 3: A transient isotopic approach

Mechanistic aspects of low-temperature (423–723 K) selective catalytic reduction of NO with NH 3 (NH 3-SCR) over an Ag(1.7 wt%)/Al 2O 3 (2Ag/Al 2O 3) catalyst in the presence and absence of O 2 and H 2 were studied using a transient low-pressure (peak pressure < 10 Pa) technique, the temporal analysis of products (TAP) reactor, in combination with isotopic traces. Preoxidized 2Ag/Al 2O 3 showed very low activity in the NH 3-SCR reaction. The activity increased tremendously after ex situ reduction of 2Ag/Al 2O 3 in a hydrogen flow (5 vol% H 2 in Ar) at 373 K for 30 min. This observation was related to the creation of reduced Ag species, which catalyze O 2 and NO dissociation, yielding adsorbed oxygen species. O 2 is a better supplier of oxygen species. Oxygen species played a key role in NH 3 dehydrogenation, yielding reactive NH x fragments that are important intermediates for nitrogen formation via a coupling reaction between NO and NH 3. This reaction pathway predominated over direct NO decomposition to N 2 in the presence of O 2. In addition to generation of active oxygen species, gas-phase oxygen accelerated transformation of surface N-containing intermediates into gas-phase reaction products. The role of hydrogen in the NH 3-SCR reaction is to transform oxidized Ag species into reduced species that are active sites for O 2 and NO adsorption. Our findings suggest that the reduction of oxidized Ag is responsible for the boosting effect of H 2 in the NH 3-SCR reaction, and also that H 2 helps decrease total N 2O production.

Selective NH 3 oxidation on (110) and (111) iridium surfaces

Ammonia oxidation was studied in situ on Ir(110) and Ir(111) under low-pressure ( ∼ 10 −7 mbar ) conditions. NH 3 does not dissociate on a flat Ir(111) surface, but surface defects and O ad facilitate NH 3 ad decomposition. High-energy resolution fast XPS measurements were used to monitor the surface coverage during reaction on Ir(110), and temperature-programmed reaction measurements were applied to reveal the gas phase reaction products during reaction. The steady-state NH 3 oxidation reaction starts between 350 and 500 K on both surfaces, which also show similar selectivity. Below 600 K, N 2 and H 2O are the principal reaction products. Above 600 K, the selectivity changes to NO and H 2O, with the exact temperature depending on the NH 3:O 2 pressure ratio. The surface population changes from NH ad/N ad to O ad around 500 K, about 200 K lower than the selectivity change from N 2 to NO observed in the gas phase. This behavior can be explained by considering the activation energies for N 2 and NO ad formation. We present a model to explain why Ir is more selective toward N 2 than Pt.

Titanium dioxide mediated heterogeneous photocatalytic degradation of gaseous dimethyl sulfide: Parameter study and reaction pathways

This paper deals with the photocatalytic degradation of gaseous dimethyl sulfide (DMS) in a wide range of inlet concentrations (3ppmv<[DMS]in<545ppmv), gas residence times (5s<τ<55s) and relative humidities (3%<RH<75%), using TiO2 Degussa P25 as a photocatalyst in a flat-plate photoreactor. DMS removal efficiencies increased with lower [DMS]in and higher τ, while the optimum RH was 22%. Although DMS removal efficiencies higher than 90% (peaks over 97%) could be obtained for at least 180min at τ=55s, RH<53% and [DMS]in<10ppmv, prolonged irradiation and/or increased [DMS]in resulted into catalyst deactivation due to accumulation of reaction products on the TiO2 surface. During photocatalytic DMS degradation at [DMS]in≥100ppmv, dimethyl disulfide, carbon dioxide and sulfur dioxide were detected as gas-phase reaction products, while solid–liquid extraction revealed dimethyl sulfoxide, dimethyl sulfon, methane sulfonic acid and sulfate as reaction products adsorbed on the exposed catalyst. Consequently, detailed photocatalytic DMS degradation pathways were proposed, starting with TiO2(h+) or OH mediated DMS oxidation and followed by CS bond cleavage, S-oxidation and C-oxidation. Carbon and sulfur mass balances were closed for 90–105% and 98–110%, respectively. [DMS]in did not have an important effect on product distribution, but interesting trends in DMS degradation products were observed as a function of RH.

Atmospheric fate of OH initiated oxidation of terpenes. Reaction mechanism of α-pinene degradation and secondary organic aerosol formation

This paper studies the reaction products of α-pinene, β-pinene, sabinene, 3-carene and limonene with OH radicals and of α-pinene with ozone using FT-IR spectroscopy for measuring gas phase products and HPLC-MS-MS to measure products in the aerosol phase. These techniques were used to investigate the secondary organic aerosol (SOA) formation from the terpenes. The gas phase reaction products were all quantified using reference compounds. At low terpene concentrations (0.9–2.1 ppm), the molar yields of gas phase reaction products were: HCHO 16–92%, HCOOH 10–54% (OH source: H 2O 2, 6–25 ppm); HCHO 127–148%, HCOOH 4–6% (OH source: CH 3ONO, 5–8 ppm). At high terpene concentrations (4.1–13.2 ppm) the results were: HCHO 9–27%, HCOOH 15–23%, CH 3(CO)CH 3 0–14%, CH 3COOH 0–5%, nopinone 24% (only from β-pinene oxidation), limona ketone 61% (only from limonene oxidation), pinonaldehyde was identified during α-pinene degradation (OH source H 2O 2, 23–30 ppm); HCHO 76–183%, HCOOH 12–15%, CH 3(CO)CH 3 0–12%, nopinone 17% (from β-pinene oxidation), limona ketone 48% (from limonene oxidation), pinonaldehyde was identified during α-pinene degradation (OH source CH 3ONO, 14–16 ppm). Pinic acid, pinonic acid, limonic acid, limoninic acid, 3-caric acid, 3-caronic acid and sabinic acid were identified in the aerosol phase. On the basis of these results, we propose a formation mechanism for pinonic and pinic acid in the aerosol phase explaining how degradation products could influence SOA formation and growth in the troposphere.

Comparative IR spectroscopic study of Pt- and Pd-containing zeolites in the hydrodechlorination reaction of carbon tetrachloride

Hydrodechlorination of CCl 4 was investigated on noble metal containing zeolite catalysts by IR spectroscopy. Both the surface species and the gas phase reaction products were simultaneously analysed. Results revealed that the reaction rate and the reaction products were different on Pt- and Pd-containing samples. The enhanced formation of ethane and the suppressed generation of methane over Pd/NaY-FAU zeolite and the formation of chloroform as intermediate product over Pt/NaY-FAU zeolite were explained by the different bond strength of reaction intermediates to the metal surface. The influence of acid sites on the product distribution was traced back to the local decomposition of zeolite framework. A combination of IR spectroscopic methods including simultaneous analysis of gas phase products and surface intermediates proved to be an excellent tool for investigating the reaction mechanism.

Gas phase reaction products during tungsten atomic layer deposition using WF6 and Si2H6

The gas phase reaction products during tungsten (W) atomic layer deposition (ALD) using WF6 and Si2H6 were studied using quadrupole mass spectrometry. The gas phase reactions products were different for the WF6 and Si2H6 reactions. No surface reactions were observed for WF6 exposures at room temperature. The WF6 reaction produced H2, HF and SiF4 at a reaction temperature of 473 K. Mass spectrometer cracking patterns established that SiF4 is the silicon reaction product instead of SiHF3. Auger electron spectroscopy (AES) measurements confirmed that the H2, HF and SiF4 gas phase reaction products during WF6 exposure coincided with the loss of silicon surface species. The Si2H6 reaction showed two separate reaction channels depending on reaction temperature. At room temperature, a temperature insensitive reaction produced SiHF3 and H2 reaction products. A second reaction produced H2 as the reaction product at 473 K. AES measurements confirmed that the SiHF3 and H2 reaction products during Si2H6 exposure were concurrent with the gain of silicon surface species. Together with previous FTIR spectroscopy and AES studies, these mass spectrometer results help to identify the stoichiometry of the surface reactions during the sequential WF6 and Si2H6 exposures that define W ALD.

BF3 Adsorption on Stoichiometric and Oxygen-Deficient SnO2(110) Surfaces

BF3 has been used as a probe of the basicity of surface oxygen anions on SnO2(110) surfaces. BF3 interacts directly with surface lattice oxygen “base” sites on SnO2(110) and acts as a reasonable molecular chemisorption probe for the basicity of thermally stable three-coordinate O2- anions by forming a Lewis acid/base adduct with these particular surface oxygen anions. However, BF3 reacts irreversibly with the more labile two-coordinate bridging oxygen on the stoichiometric surface, and no distinctive BF3 desorption feature is observed in thermal desorption that can be used to provide a measure of the basicity of bridging oxygen anions. These results are indicative of an inherent limitation in the application of BF3 thermal desorption measurements as a simple probe for the basicity of surface oxygen species of limited thermal stability. The presence of bridging oxygen on the stoichiometric surface does gives rise to gas-phase reaction products (HF and F2) in thermal desorption that are not seen on the more oxygen-deficient surfaces. For all surfaces, some BF3 dissociation is observed, which results in the slow build up of surface boron and fluoride during consecutive thermal desorption runs.

Gaseous and Particulate Oxidation Products Analysis of a Mixture of α-pinene + β-pinene/O3/Air in the Absence of Light and α-pinene + β-pinene/NOx/Air in the Presence of Natural Sunlight

The gas and particle phase reaction products of a mixture of the atmospherically important terpenes α-pinene and β-pinene with the atmospheric oxidants O3 and OH/NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of α-pinene and β-pinene in the presence of O3/air, and the daytime oxidation of a mixture of α-pinene + β-pinene with NOx air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for ∼74 to ∼80% of the reacted α-pinen/β-pinene mixture carbon. Measurements show that a number of reaction products were found in both O3 and NOx system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.

The Chemical Reaction of Diethyl Carbonate with Lithium Intercalated Graphite Studied by X-Ray Photoelectron Spectroscopy

The chemical reaction of diethyl carbonate (DEC) with lithiated graphite was studied in vacuum with X-ray photoelectron spectroscopy (XPS) using the temperature-programmed reaction methodology. DEC molecules were condensed onto the sample surface at 120 K, and XPS spectra were collected while warming the sample in increments of 30 to 620 K. For purposes of comparison, surfaces of pure metallic Li, lithiated graphite and bare graphite were studied using identical procedures. The reaction path of DEC on surface was very similar to that on pure Li except for small shifts in the temperature where the same reaction occurred. In the range of 180-270 K, changes in the charging of the surface layer as the DEC evaporates/reacts on the surface make it difficult to determine the reaction products. In the 270-390 K region, the C/O stoichiometry of the surface layer decreases from 1.67 to ca. 1.0, and reaction products on the surface are most probably lithium methoxide and lithium oxalate Ethylene and/or CO were the only clearly identifiable gas-phase reaction products. begins to form at ca. 330-360 K from the decomposition of oxalate. Methoxide is thermally stable up to about 450 K, near the melting point of lithium. The final reaction at 390-620 K is decomposition of all organic carbon-oxygen species to form and CO. Our experiments thus indicate that the exotherm observed at ca. 120-140°C in the calorimetry of Li-ion negative electrode materials is most probably the decomposition of the solid electrolyte interface layer into and CO, and not into © 2002 The Electrochemical Society. All rights reserved.

Catalytic decomposition of SiH4 on a hot filament

The products of SiH4 decomposition on the surface of various filaments were directly detected by using vacuum ultraviolet (VUV) photo-ionization mass spectrometry under collision-free conditions. SiH2 and SiH3 were detected at filament temperatures of approximately Tf∼1300 K, where silicide formation on the filament was observed. At higher temperatures, the SiH2 and SiH3 signal intensities decreased and Si atom signal increased. It was confirmed that the Si atoms were the main species desorbed from the tungsten filament at Tf>1700 K. H atoms were also detected as a direct desorbed species from the filament by using the [2+1] resonance enhanced multi-photon ionization (REMPI) method combined with time-of-flight (TOF) mass spectrometry. Gas phase chemical reactions of SiH4 with desorbed radicals (Si and H atoms) were also investigated. Si2H6, Si2H4 and Si2 could be detected as products of gas phase reactions. A chemical kinetic mechanism starting with Si+SiH4 and H+SiH4 reactions was proposed to explain the formation of Si2H6 and Si2H4.

Ozone and Low Concentrations of Nitric Oxide have Similar Effects on Carbon Isotope Discrimination and Gas Exchange in Leaves of Wheat ( Triticum aestivum L.)

Summary Field-grown spring wheat (Triticum aestivum L. cv. Albis) was exposed in open-top chambers to three levels of ozone (O3) with or without addition of 8 ppb nitric oxide (NO), resulting in six different mixtures of ozone, NO, and their gas-phase reaction product nitrogen dioxide (NO2). The aim was to study the effect of the different mixtures on leaf gas exchange and carbon isotope discrimination in flag leaves. From emergence to the first appearance of senescence symptoms, leaf conductance to water vapour (gs) and net CO2 exchange (PN) was analysed together with stable carbon isotope ratios of the plant material (δ13Cp). Relative to the control with low ozone and no NO addition, mixtures with either additional ozone or NO added to charcoal-filtered air caused an increase in gs. but no change in PN , resulting in increased sub-stomatal CO2 concentration (ci). In both cases δ13Cp was not significantly changed. This indicated the occurrence of similar effects of ozone and NO on enzymatic reactions of carbon fixation. When applied in combination with medium or high ozone levels, the effect of NO addition was smaller than in combination with low ozone. These results suggest non-specific responses to reactive oxygen-species generated by both ozone and NO. It is concluded that the effects of NO in the low ppb-range are mainly due to shifts in gasphase chemistry at the leaf-atmosphere interface, and that they are negligible in pollution climates dominated by ozone.

Synthesis of Organic Compounds from Mixtures of Methane with Carbon Dioxide in Dielectric-Barrier Discharges at Atmospheric Pressure

The entire range of gas phase reaction products, depending on the composition of initial binary mixtures of methane and carbon dioxide in dielectric barrier discharges, has been determined (saturated as well as unsaturated hydrocarbons and oxygenated organic compounds). The macro-kinetics of the basic chemical pathways of the system under consideration has been investigated. This system is found to display a strong feedback effect (positive or negative, depending on the initial state of the surfaces, as well as the chemical composition of the feed-gas mixture). It is demonstrated that these properties undergo significant changes during operation, due to surface modification processes (polymer film deposition, its oxidation or reduction). They are found to exert a considerable influence on the chemical efficiency of the discharge (for example, on the absolute and relative chemical yields of the reaction products), the Lissajous figures appear to be a sensitive tool to monitor the operation conditions of the discharge.

Graphite Processing With Carbon Retention in a Waste Form

Conversion of waste graphite into a stable waste form acceptable for long term storage and disposal was considered both theoretically and experimentally. A self-sustaining transformation process of graphite composited with suitable precursors was studied. The powdered precursors that were used were used were: Al+SiO 2 (1), Al+TiO 2 (2) and Ti+SiO 2 (3). Numeric thermodynamic simulation was performed. Equilibrium temperatures and chemical compositions of reaction products were determined for a wide range of component ratios in the source mixtures. The highest temperatures (up to 2300 K) were observed for precursor type (2). Precursor type (3) demonstrated a minimal rise of temperature of up to 1900 K. Regions of compositions with complete binding of all chemical elements as well as production of stable final products were found to be rather narrow. About 10 – 13 wt.% of carbon can be processed in composition with given precursors. The gas phase reaction products were studied to minimize carry over of radionuclides. Carbon monoxide was shown to be the main component of the gas phase. The self-sustaining synthesis process was conducted in ceramic crucibles at ambient pressure in an air atmosphere. Batch masses ranged between 0.1 – 1 kg. Best results were obtained for processing of graphite composited with Al and TiO 2 . XRD analysis has identified titanium carbide and corundum in the waste form produced. These experiments confirmed that carbon can be converted completely into a stable waste form.

Application of gas chromatography–cryocondensation–Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry to the identification of gas phase reaction products from the α-pinene/ozone reaction

The gas phase reaction of α-pinene with the atmospheric oxidant ozone was investigated by using the capabilities of both gas chromatography–cryocondensation–Fourier transform infrared spectroscopy (GC–FT-IR) and gas chromatography–mass spectrometry (GC–MS), for the identification of the reaction products formed. The reaction was carried out in a flow reaction chamber from where the compounds were sampled on Tenax-containing adsorption cartridges. The reaction mixture was injected onto the column after thermodesorption and analyzed using both GC–IR and GC–MS. Twenty compounds could be detected, including the reactant α-pinene and it’s impurities tricyclene and camphene. Eleven compounds were identified by spectra comparison with either reference data or spectra obtained from commercial standards. Four compounds were tentatively identified from their IR and MS spectra, while from the remaining two compounds the nature of basic functional groups could be established.

Investigation of the Heterogeneous Reactivity of HCl, HBr, and HI on Ice Surfaces

The interactions of hydrogen halide gases (HX = HCl, HBr, and HI) with thin ice films representative of atmospheric aerosols have been studied using a Knudsen cell reactor coupled to a Fourier transform infrared−reflection absorption (FTIR−RAS) spectroscopic probe. The gas-phase uptake and reaction products resulting from the exposure of hydrogen halides to ice surfaces over a wide range of temperatures (110−210 K), hydrogen halide partial pressures (5−1000 × 10-7 Torr), and ice film thicknesses (10−100 nm) are reported. Studies of HCl and HBr showed efficient reactions on crystalline and amorphous microporous ice films at 110 K to form H3O+ until reaching coverages ranging from (5−20) × 1015 molecules cm-2, after which the rate of reaction dramatically decreased. The uptake of HCl on hexagonal crystalline ice at temperatures representative of the lower stratosphere and upper troposphere (180−210 K) was found to depend strongly on HCl partial pressure. Over the temperature range studied, exposure of ice to HCl partial pressures below the HCl equilibrium partial pressure at the liquid/ice coexistence point resulted in uptake limited to (3.5 ± 1.6) × 1015 molecules cm-2. In contrast, exposure to HCl pressures larger than the HCl equilibrium partial pressure resulted in unlimited uptake. HBr and HI were efficiently and continuously taken up by ice surfaces (γ ≥ 0.02) over a range of atmospherically relevant temperatures (180−210 K). Although crystalline hydrates of HX:H2O are stable over the temperature range examined, the incorporation of hydrogen halides into ice always resulted in the formation of amorphous HX:H2O product layers with the exception of HBr uptake at high flow rates (flow rate ≥ 3.1 × 1015 molecules s-1) which resulted in the formation of a mixture of crystalline hydrates.